Funny, I tried the dealer. They said they don't sell the plastic molding, I'd have to purchase the entire window and molding as a package for the quarter panel.
$200, plus installation. I just laughed as they told me. Not their fault obviously! Unreal though. Guess I'll try some double sided 3M exterior tape and glue!! $15.
My wife's 04 RX330 passenger side rear quarter panel window molding also GONE last week, at 1st I thought someone jacked it but later found out it is probably flew away while driving; what a defect from Lexus.
Called couple of junk yard places and checked ebay with absoluetely no luck, finally called total of 3 Lexus dealerships in Southern California and purchased a complete set with no choice; because it only sold as a complete assembly set; what a rip off.
For those who interested in replacing it anyway, the part no. is 62710-48170 ranging from $150-185 depending on which dealership you are calling; surprisingly they all have this part in stock, must be a highly demand popular item.
Installation is about $50 outside the dealership, ***highly recommended***. I was trying to do-it-myself and ended up broke the original glass and made a mess every where. I had to call professional help to finish the job, what a shame.. it's easier than it looks and requires special window adhesive..
have fun and good luck with this project...