You could call up Kevin Marti, and for a price, he could tell you how many were built. Probably pretty rare, rarer than a Sprint!!
I suspect the Maverick police package was in responce to Chevy's 9-C-1 Nova package. Our county Sheriff's Dept ordered a 77 LTD II, specing the largest engine with a 4 bbl carb. When it came in, it had a 400 with a 2 bbl! They refused to take delivery, saying that it didn't meet their specs. I knew the guy who ended up buying it, he got a great deal on it. For a 2bbl, it would run pretty good. The Sheriff's Dept then ordered a 9-C-1 Nova. It came with a 350 Corvette engine, 4 bbl, true dual exhaust, and bigger sway bars from a Camaro. It was a hoss! I was friends with the Sheriff in office at that time, and told him that when the county got through with it, I wanted it! He was defeated the next election, the car was totaled in a chase, and I never did find out what happened to it after that.