I've gotta agree with the RockAuto.com suggestion. Of course you aren't going to get OEM Lexus or Toyota parts, but the replacements generally are as good in quality because they all have to go through the same specifications as each other to make it on the market.
Currently driving a 93 GS, not in a hurry to sell, but have been considering for quite sometime now an IS350 when I do decide to move on. How are you owners liking them?