Same here. I have just begun searching for this part and even ordered something (which turned out to be wrong), but so far no luck!
EDIT: Just found a product on Amazon: GreceYou 5M Universal Self Adhesive Auto Rubber Weather seal that looks very similar and like it might work. All Toyota and Lexus parts are integral to the cowl and ~$500.
AUTOXBERT 4M/13Ft Automotive Weather Stripping Rear Windshield Seal Trim Universal Y Shape Rubber Sealing Strip Trim Cover Window Edge Moulding Trim Panel Sealing https://a.co/d/eNx3Rmm
I think it will stick up higher than OEM, but that’s $12 versus $450.
Any updates on a solve for this? My weatherstripping is very loose and the dealer didn't know how to fix, so looking for some inexpensive alternatives.