IBM spun out their keyboard division decades back when they they spun out printers (into Lexmark). The current inheritor of the keyboards is Unicomp (having bought it from Lexmark/IBM): https://www.pckeyboard.com/

It's a bit cheaper to buy from them than to pay for an antique on eBay.

Also, there's a wave of mechanical options from more recent companies like Das Keyboard or the various DIY kits with choose your Cherry switch adventures.