Frog,
The Mustang has not even been certified for a year yet. There are so few in existence right now that there is very little opportunity for TRTO's to make money offering a Mustang TR. You're just not going to find many places that can do it yet. I can't imagine why you want a TR for an aircraft that is so scarce unless someone has offered you a job flying one, but then I would assume they'd know how and where to get you type rated. Unless you have a Mustang job offer in hand, I would suggest taking a Bravo or other Citation TR and then see about getting differences training later if you get a Mustang job.