Hodgdon 777 2FG will work very well in the T/C 54 cal caplock and is widely available. You will also find it's exceptionally clean as compared to pyrodex and BP. With 777 2FG, reduce your loading data by 15%.(100gr becomes 85gr and so on).
I would shoot777 over Pyrodex every day of the week and twice on Sunday.
Goex is a very good Black Powder. However I prefer Swiss BP over every other BP. Swiss is the most clean, powerful and consistant of all of the BP's I have used. I shoot about ten pounds of Swiss every year.
Try
www.powderinc.com You will need to order at least five pounds, but even with the hazmat and shipping you will be saving substantially over retail.