Well, beyond the fact that they both go bang (function) they are different enough for the RCMP lab to say that the Black Special is not in any way a Sig 550, and therefore is not prohibited in this country. I don't think there are any real 550's in civillian hands to compare the Black Special to. (Note, this type of question ellicits lot's of angry responses every time it comes up) As far as specifics go try TSE (Redleg or JR) they may be able to help you, but they may not be in a position to do so, due to import licensing concerns. These particular rifles are available only in Canada, and they are the guys who got it done.