Does anyone know of a supply source for the old ST90R158Q6 processor?

[Bolan69]

..

[Tesla DeLorean]

Octopart is generally pretty good at finding things, other than that you'll need to find a parts broker you trust

https://octopart.com/st90r158q6-stmicroelectronics-723513

Someone on AliExpress claims to have stock

https://www.aliexpress.com/item/4000464038012.html