I found polyurethane sway or stabilizer bar bushings on eBay and ordered a set for the rear bar to reduce understeer and body roll. $28 shipped. I will update with a review when they are installed.
Note with Polyurethane bushings it is best to use poly compatible grease when installing them to prevent squeaking and binding. Prothane makes the grease and it is on eBay for about $8 for enough to do your installation.

The seller has both front and rear bar bushings. They provide the inner dimension which I confirmed with my digital calipers and also the compatible OEM part number, which also matches up!
The seller is called Siberian Bushing and is in Russia. They have excellent feedback.

This is the listing title for the rear you can use to search

Set of 2 PU Bush Rr Susp. Swaybar fits RX450H RX270 RX350 ID 21.7 mm

They provide this description:

Siberian Bushing Polyurethane bushing, Sway bar, Rear suspension Lexus RX270 / RX350 / RX450H GYL15L, GYL15R, GGL15L, GGL15R, GYL10L, GYL10R (2008.12- ), I. D.= 21,7 mm.

High-quality bushing of improved original design. Produced since 2000 from elastomers based on traditionally used polyurethane. All sizes match the original ones. Ideal for tuning and repair.OEM compatibility: 48818-48070

 

Good find. I have kept up on reviews of poly bushings on various Lexus models. [Going all the way back to 98 GS. Lexus even changed some components in 02 but still kept the rubber]. The initial response from mostly all users has been positive but over time some have reverted back to the OEM rubber as they miss the compliance. The feel is totally subjective and I hope you like the stiffness you are looking for.

Salim

 

Im wait for your update review.

 

I ordered a set of Universal Energy Suspension Sway Bar bushings, black, 21mm, part no. 9.5125G from 4Wheel Parts for $20.
Update: The bushings are actually Prothane 191164-BL and the bracket bolt spacing is not quite wide enough. Prothane 191120-BL should do it.
They have a store near me so the shipping is free.
If I measured correctly they should fit the rear of our 2012.
I haven't wiggled up to the front bar bushings to measure the bracket bolt spacing/bar diameter, yet.
If they do not have the exact size bushings a smaller diameter bushing can be bored out with a drill press to the exact size.

 

Seems the Prothane chart is wrong, the 191120-BL bushings also use the "A bracket" which has the narrow bolt spacing.
The closest Prothane "B bracket" bushing is a 13/16" 191131-BL which can be bored out to 21mm.

 

I suspected they would not fit. A few years ago I researched other poly bushings that may fit and bought a couple different types, one I think was for a Honda S2000 but none fit inside our brackets, they were usually too small or moved around too much.

However, the Siberian bushings arrived last week and are a perfect fit. They even supply the required grease for inside the bushings. They do stiffen up the rear a bit, reducing side to side body roll while only slightly increasing harshness, which I soon adapted to and stopped noticing. I will leave them on. They are worth the reasonable price.



Now to replace the rear trailing arms whose bolts by the rear shocks are a real pain to remove while the car is on floor jacks. I may have to have the local gas station repair shop do it instead as I think it needs to be on a lift to get sufficient leverage to break those bolts loose. Ugh!

 

What's wrong with the control arms and how many miles?
Are the large bushings in the front end bad?
I don't have any noises and ours look ok, is there any visible deterioration?

 

Bad bushings that make noise and have lots of cracks. 75,000 miles. Do a search, this is a known wear item. Noise is the primary complaint that leads to replacement.

 

Ours is a 2012 with 87k, no noise or cracks in the bushing.
From searches I think there was an improved bushing used in the 2012+.
How long did your shocks last?
Ours are the OEM shocks and I think I'll have to remove one end to see if they any good.

 

The rears are famous for leaking on 2010-2012 models. If the lower half looks wet or darker than the top, you have a leaky shock. At least they are inexpensive to buy and easy to replace, only 2 bolts. The front struts last much longer.
Or if you think the ride has become worse, then get new ones. The rears affect your ride more than the fronts.

 

Inspected the rear shocks and they look fine, no discoloration.
They still have gas pressure, too.
I'll check them again at 100k.
Not sure if they are OEM, there is nothing on them, except stamped in the housing is a warning about being under pressure and don't puncture the housing.
There's also a blue line around the lower section about 3/4 of the way up.
Our 2002 Excursion had 104k on it when we got it and the gas shocks would compress, but not extend without pulling it.

 

The Prothane 19-1131-BL bushings work fine for the 21mm rear anti-roll bar.
They are speced at 13/16", but my 21mm Forstner bit dropped right thru, so no boring required.
They come with a packet of grease in the box.
Lexus uses rather robust mounting bolts to hold the anti-roll bar bushing brackets.
The Prothane brackets need to be drilled/ground/filed out to 1/2" in the center of the slots to clear the mounting bolts.
The ride smoothness hasn't changed, but when turning sharply the rear end stays flatter.