I think all the brands, gate, aster, leviathan and perun do v3s which do away with the trigger block.
The perun is the cheapest at around 60 quid.
I've realised your moving the trigger out of the gearbox so none of those would work for you.
Perhaps more details about what you are mounting your trigger in?
If it's from scratch you could hack up an old gearbox section and a normal trigger and block with a bog standard MOSFET.