Whilst buying one may be out of the question, it is possible to build a PDP-8 "clone" from raw TTL. I know this was done on at least one college course, and there are books out there to support it...

Will be going to see this

Even the SBC6120 is getting hard to find , I waited for two years before one became available and that's the one with no front panel. But it is a great beast...