The 292c uses semi-rare LF13331 switches (as do several vintage video games, which is where you can sometimes find this part) and Mark Verbos has done a version using the easily-available 4016 quad switch.
I haven't checked the 13331 specs but the 4016 is listed at .4% distortion. I wonder if any golden ears would detect such a difference (between that and a hardware switch)...
www.simple-answer.com/DIY.html
