Why not just visit your local restaurant supply store?, that's probably where they get it from themselves. I highly doubt the ballparks have an actual recipe for that stuff, it more than likely comes in pre-processed.
The web site Serious Eats had a recipe for the ultimate nacho cheese sauce which called for a container of that "Pub Cheese" (the kind you spread on crackers), along with a can of condensed milk and hot sauce. I tried it and wasn't blown away by it personally. It had more of a pinkish orange color to it than that neon orange color I'm used to seeing. But it might be a starting point to a better recipe.
Or maybe try something totally different. One of the restaurants I used to work at made these fantastic chicken nachos with fried tostada shells. For something simple, you could take the fried tostada shell and top each with a slice of colby cheese or provolone cheese - both are shaped round like the tostada. Then top with some sliced pickled jalapeno, and throw them under the broiler. When they come out, cut them in half so they look like half moon shapes. Then get a large bowl and put some shredded lettuce in the middle, and a scoop of guacamole, fresh pico de gallo, and sour cream on top of it. Then arrange the nachos around this in the bowl for presentation.
