Another option no one mentioned is to see if your family is a sept of a larger clan. If so, you can wear that tartan as well.

A last (and most expensive) option is to have a NEW tartan designed and woven for your clan. Unless you have approval of a clan cheif (if there is one), it will likely be categorized as a 'fashion tartan', but that won't matter, as you're the one who designed it, and you'll be the one wearing it.