Captive Nuts and Bolts
 

You can try here also...

Screws:
http://www.webstore.com/item,pgr,OEM-TOYOTA-CAMRY-LEXUS-AIR-FILTER-BREATHER-CLEANER-BOX-COVER-BOLT-SCREW-2AZFE,name,43285635,auction_id,auction_details

Nuts:
http://www.webstore.com/item,pgr,OEM-TOYOTA-CAMRY-LEXUS-AIR-FILTER-BREATHER-CLEANER-BOX-COVER-SQUARE-NUT-2AZFE,name,43286123,auction_id,auction_details

I put it on mine and it's perfect fit.

Thank you Noozboy, your advice was right on the money. Replaced wife's air filter on her es and sure enough lost a bolt. Shocked to jump online and find you can't buy them. Checked eBay and they were there, but seemed like a rip off. Saw your post, headed to Home Depot, bought the m5 25mm screw and washer and voila, problem solved. Fit perfect and easier to remove and install than the original hex bolt. Thanks for sharing Noozboy, you made my evening and saved me a ton of grief.

Update on captive bolts
 

You can find those captive bolts on eBay at the following link.

Genuine OEM Toyota Lexus Camry Airbox Cover Bolts / Screws/ Lid

Genuine OEM Toyota Lexus Camry Airbox Cover Bolts

Hi Noozboy - I just checked replaced the engine air filter a couple weeks ago (replaced cabin air filter as well) for the first time and I found the screw in behind the air box (closest to the driver) was completely missing...nothing holding it together. On the front side nearest the front of the vehicle was one screw with no nut or anything holding it closed/sealed. So absolutely nothing was secure the top of the air clean box to the bottom (and we've taken it to the dealer multiple times over the last couple of years.
With that said, I saw your solution and just bought some M5 25mm screws. But now I need to get the washers. What size of washer do I need to get, and how does that help the screw seal the airbox? I thought the screw needed a nut to tighten from underneath. Again, I'm completely new to this, so any advice would be helpful.

Thank you!

The bottom of the box that is stationary is threaded to accept the bolts. The washers are about a half inch in diameter and are key to getting a good seal. Washers will slide into a slit in the top of box, then bolts pass through and tighten. Washers help lock everything together. Look at the top removable part of box to see how washers slip into the slit in the plastic top box.

Thanks BlackLexRX. I will take a look tomorrow evening. I'm wondering if something happened to the front side location, because when I looked at the screw/bolt that was down all the way through the bottom of the box, it seemed very free and was not screwed in tight to anything. If it's supposed to screw into the bottom of the box snugly, I'll make sure I double-check that closely. I'll let you know if I run into any issues. Thanks again!

The washer helps set the depth for the little bolt to be able to get into the threads below. I've changed my filter a couple times now, so I'm used to getting that washer in there correctly. First time I tried, washer was above its slot and no matter of tightening bolt would allow it to grab threads below. Once I got the washer into its slot, bolt tightens.

I bought mine here.

http://m.ebay.com/itm/GENUINE-OEM-TOYOTA-SCION-LEXUS-AIR-FILTER-ELEMENT-BOX-COVER-BOLTS-SCREWS-NUTS-/221772434907?nav=SELLING_ACTIVE&skus=Type:1%20Bolt&varId=520619453808

Replace captive nut
 

Went to a lube stop and they broke the bolt off in the captive nut that holds the air filter Cover

I used a tie wrap.
I am Surprised Toyota spent the time to make it so complicated. Maybe they sub'd that piece to Germany

Just followed that link; :-( the seller is asking for $8.00 for one nut.

I am most likely going to just go to Ace hardware and buy some M5 stainless steel nuts and epoxy them into the spot.

Cheers

Not sure if you solved the problem. It just happened to me; but there should be a nut embedded in the bottom part of the air cleaner housing that the screw will attach into. It appears to be a common issue with many Lexus & Toyota vehicles that the nut drops out. Cheapest online replacement is about $8.00 currently for one nut. Toyota/Lexus wont sell you the screw/ nut by itself, so you have to buy the whole housing which is $240 Toyota branded for a Sienna; ~$700 for a Lexus RS330 one. Basically the same product just with different labels.

check with the dealer; N1 part carries a footnote that it is part of the air cleaner housing and is not sold separately. Majorly suck from a design point and ownership perspective.

my 04 highlander- one nut location is held on/together with a tie wrap for the last 2 years , design may be different, works fine

Replace Filter with permanent one, less frequency on cleaning.