2019 RX 350 F Sport: 2nd owner. Bought it with 1 locking lug nut on each wheel. Have key, no problem. No need to have lock on it. Want to replace with oem lug nut. Want to get it right...Dealer part? Or Amazon replacement? Discouint tire guys didn't know. Thank you all!

Try the dealer, either an online discount place or call your local one for a price. Or there are plenty on eBay.
This size is used by many different Lexus and Toyota vehicles.
The size is M12 X1.5
One of the part numbers used, although it may be superceded is: 90942-01033
https://parts.longolexus.com/oem-par...5MeMq8GrEhFuPg

thank you!