The 45 Colt is not that picky on powders. It's a basic straight walled case, so almost any pistol powders will work. You faster burning powders will be good for lighter powder charges with decent velocity. Your slower burning powders will be good for slightly higher speeds, but with a higher powder charge.
Trail Boss is a decent powder for a lighter load, but near impossible to find. Since you can not find it, I'd highly recommend a different powder.