On eBay you will find a company in Georgia that rebuilds the Pioneer changer for the Lexus. He may have one for sale. Also I think I have seen adapter cables for the RX300 that will alllow you to hook up an aftermarket CD changer to the original wiring.
the rx300 radio doesnt even have a 12 pin cd changer plug on the back of it so it would be impossibe to use the blitzsafe 12 pin adapter and an after market changer. . when blitzsafe first made the adapter they only had two lexus radios a 98 pioneer and a nakamichi so they thought all other radios connctors were the same.on all lexus models which is far from reality. used factory changers are now 5 years old so used not a good deal either. i have new in the box rx300 changers with 5 years warranty at 75% off list price of the cd changer kit price from the dealer. the kit includes the glovebox panel that has to be changed to accomodate the changer in the ceiling of the glovebox. email me at email@example.com for more info.