Some enthusiasts have made custom PCBs for Topre and Niz switches, even columnar ergo. I've not seen the ErgoDox layout specifically, and I dunno how to source individual switches though.

There is also the XVX Whisper switch, with has a Topre-like mechanism for Hall Effect keyboards: with a magnet under the dome. You could buy pack of switches but reviews say it is mushier than Topre.