That tap is a 1 & 3/16-16 special inch tap. A supplier such as Marshal Tool will have it. Enco, Grizzly, Harbor Freight, and the local hardware stores won't have it.
If you have access to a lathe you could make your own tap from a piece of good steel (4130 cms...). Since it is to tap aluminum (7075 T-6 usually) your tap need not be hardened for a one time use, just sharp.
Sorry I don't have one of those taps.