on different websites pertaining to Tartans and Clans, I have the understanding that you can wear any clan tartan of an allied clan. For example, my Clan is Maxwell, and the Maxwell Clan has several allied Clans, and from my understanding, I could wear the Tartan of any of those allies.
I personally, wouldn't feel comfortable wearing another Tartan, even if it is allowed, but in your case, you don't have much of a choice. If my understanding is true, then what you need to do is find the allied Clans of your surname, and then take your pick.