UCCNC has a plasma software.
Unkown to me what it is like though. Have a good read of the forum over on the cncdrive website. Their controllers are available in the UK.

I looked at Mesa for a cnc but the ones I wanted I couldn't get without paying silly money tariffs.

Didn't want a basic step/dir I/O card (looked like all you could get back then over here), may as well have just got a pport pc for what you got.
UK has got even worse in terms of product availability (and overpricing) in the last 4 years.
Majority of my mill electronics are from Aliexpress with the exception of my controller section.