Welcome to ribnet!
What bit(s) do you need? Almost any "single lever" box will work the throttle & gears (they all use the same internal mechanism), it's the plug on the end of the electrics that will be the pain.
Having said that, if you have a gubbed box with OK electrics, it's a relatively easy job to swap the cable.
Alternatively if you have a manual start manual tilt / trim engine, all you need to do is run 2 wires for the deadman switch, and so any box will do. I think Yam do a "basic" box with a built in deadman switch & a few m of cable. New only about £70 odd last time I checked.
A couple of places I would maybe try for a used box are DA in Newport -on-tay (although more likely to get a Yam box off him) and Ardoran up by Oban, who are Suz delaers.