Adaptor for Monobloc Kitchen Tap Inlets , Where to Find?

[EdF]

I bought a new ex-display kitchen monobloc mixer tap from Jewsons when they moved showrooms last summer. Unusually, it has 15mm to 12mm brass adaptors in the inlets, but one of them has part of the lip the 'O' ring sits in broken off. I can't find any way of buying another (all the plumbers merchants scratch their heads at it) and I don't really want to resort to PTFE tape and sealing compound. The flexible hoses don't go up to 15mm, only 12mm. I haven't had any luck in finding the maker (nothing on the tap) and Jewsons can't help. Anyone seen such a thing used and know which maker uses them? Thanks!