Well, I am not the most successful of social animals so I essentially ended up ordering cheap used instruments and ending up more or less lucky. I chose pretty early to play CBA and that did limit my tryout possibilities with random acquaintances quite a lot. Also Germany is sort of the borderline between C system and B system, so that reduces your chances by another 50% once you are hooked on one system.Elsewhere!
The best thing I've found is to get someone in real life - a new accordion friend or a teacher - to lend you a few of their instruments to give you a better idea. I'm hopeful Yorkshire isn't uniquely fraternal in that regard.
Otherwise you end up down online rabbit holes and it all gets a bit intense as the oxygen depletes!
A recent gathering of accordionists I was at had an unusual amount of CBA: 2 of them C system, 2 of them B system.