I suggested egun.de on the other thread where this was raised. I'd be a little wary of one thing though, and that is that some of those German ring sets are pretty specific to a particular scope and where it will sit - especially those designed to go around the objective bell. Of course, if you have a scope with a large objective bell you also need to consider whether you'll be able to tip the scope forward enough to detach it, which is often the reason it seems for having the front ring there. Scopes with a rail underneath give you a bit more leeway fore and aft, and might avoid such issues.

FWIW when I wanted to change scopes on my drilling I bought a scope with rail and the feet to suit, via egun.de, and had the feet modified to fit. This work was done by a German-trained gunsmith, but wasn't outrageously expensive. Doing it yourself would be a case of getting out some bearing blue and fine files, and perhaps doing a bit of building up with welding, as was mentioned above, but I preferred to have someone better trained than me to do it. It has worked very well, and now I have two scopes fitted for the gun, one and a spare.

I'll take some photos later if you like.