This is probably a dumb question but I haven't found a satisfactory
solution...

I have some surface mounted equipment (e.g. heating controller,
security controller) into which I must terminate some low voltage
(50V) cables (e.g. RS485, PIR sensor connections). The equipment
enclosures have knockouts on the underside through which the cables
enter.

The cables are run within dry lining. What is a neat way to bring the
cable out through the plasterboard and up into the equipment? I could
simply drill holes in the plasterboard and thread the cable through but
this wouldn't look nice. I could have some 20mm conduit coming out of
the wall and up into the knockouts which might look a bit better. A
surface-mounted junction box (about 250mm width x 90mm height) with
rear-entry knockouts occurred to me, but I can't find a decent source.

Does anyone have some neat ideas?