https://www.vdb-waffen.de/de/waffenmarkt...mp;o=neu&v=

It's worth keeping an eye on this website.
MSch didn't produce a 6.5x55 but it's possible a rifle may have been rebarrelled/chambered, though I understand it's not a simple matter to do this due to the bolt face. But I'm not technically knowledgeable in this matter.

It's very difficult to find early 7x57 MSch's much more likely to drop on a 1950-60's MSch GK model in that cal. indeed, one is shown on the website above, although I think it's a bit pricey.