I agree that Anglo concertinas usually appear in C/G or G/D configurations but can be special ordered in other configurations if that's what you need. I have a Morse Anglo that's configured F/C as well as a G/D one.

It is theoretically possible to play songs in other keys with the standard configuration concertinas but it does require learning new fingerwork patterns, some of which are arkward.

Cheerily,
Charley Noble