I'd say that two major home platforms were Spectrum (rather, its many clones like the Pentagon) and BK series (BK-0010, BK-0011) -- market was flooded with former and the latter was mass-produced and could be actually bought in a shop. There's demoscene for both of these, see f.e. (Insult gigademo for the BK) and (showcase of several Spectrum demos from Assembly'2011).
The UKNC (on the screenshot) was an educational machine and I'm not sure how many were sold to general public; the DVK series (screenshots earlier in this thread) was a professional machine and generally wasn't available to the public at all. Of course, either could be 'obtained' if you really wanted it...
