Update: ~£30 for these Fulcrum RM16-TA12142 adapters from http://Lordgun.co.uk (Cheeky domain as they're Italy-based).
They arrived and after a bit of a fiddle installing (thread is reversed) they seem to work as expected so I now have 700C wheels on my Tripster again with road tyres and the 650Bs will stay for graveladventurehappyfuntimes.
On that note, if anyone needs the 135mm spacer for a set of Fulcrum thru-axle road wheels, let me know.
Anyone know if you can swap rear axles in Fulcrum thru-hub road wheels so they will fit wider frames, ie. 135mm to 142mm.
I don't know the wheel model but it's a straight pull CenterLock model and the current thru-axle has wrench-flats so I assume it's able to be disassembled for swappage...