Astrolux s43s rubber button cap

A mate brought his light around to fix , an astrolux s43s. It is missing the rubber button (still has the surround)
I see bg sell them (or at least thats where a link from reddit sent me when someone had the same problem), for £5.67, but they want a crazy £9.20 postage!! However the q&a say it won’t fit an s43 :person_facepalming:
Just wondered if anyone could help out, or find one much cheaper.
Worst case scenario I think he’ll have to somehow make one, it won’t be waterproof, but it at least would be covered up.