You could always claim Clan Chattan. That was much less a family clan than a confederation of families.

Or you could ask Bear@bearkilts, also known as "The MacBitseach of Clan MacBitseach" to let you join Clan MacBitseach. (MacBitseach is Irish Gaelic for son of a bitch. http://macbitseach.blogspot.com/) I don't think he has an official tartan, but the Celtic Pride would work. :P