mcdhu,
If all the above fails:
You mention "the usual 2 keys". Just in case that is a typo, and you meant the "2" key, on an English keyboard the @ is normally between the semicolon and the Enter keys, and used in conjunction with Shift.
I don't recall seeing a keyboard with the @ anywhere other than there or the 2 key, so it might be a case of trying various combinations of Ctrl, Alt, Shift etc.