were can i get chambe adapters
A couple of years ago I bought a chamber adapter for 30/06 to fire 32 pistol - 32ACP, 32S&W Long or 32H&R. The 32ACP and H&R ammo is too expensive down here to be a low cost option but the 32S&W long is good price and works well - accuracy is good out to 50yards. I've tried 32ACP but it was erratic due to inconsistent performance due to leakage from the low pressure rounds. 32cal is 0.312" and it fine for a 0.308" bore. I don't recall the brand but they made them also in 308 (none available from the importer here at the time otherwise I would have bought one of those too).
I recall seeing a 223 to 22LR adapter by the same manufacturer.
Many, many years ago I remember seeing ads for 30/06 to 30carbine adapters but that was a long time ago.
There are a few suppliers of shotgun adapters of various styles and cartridges - some are an un-rifled insert, and some include a short section of rifled barrel. I have 12ga/22LR and 12ga/357mag adapters but haven't tried them yet.
I haven't seen anything else in any other military cartridges. I don't think there are any common pistol cartridges that could be used in a 8x57 for example.