Looks like you need Lexus P/N 81615-87705. They look to be still available.
https://parts.lexusofpleasanton.com/p/Lexus_1991_LS-400/SOCKET-WIRE-SUB-ASSEMBLY-FRONT-TURN-SIGNAL-LAMP-BODY-SPOT-LAMP/63367916/8161587705.html
You don't have to buy it from the link above.
I don't know why this isn't a more common, "get it anywhere" part.