Being the C-3 was never considered a performance transmission I'm doubtful anyone ever made a deeper version. Some things to consider are ground clearance. Pinto's, especially with 13" tires, are rather short, and a deeper pan might wind up becoming a damaged pan. Also, unless you lower the pick up point (that unfortunately is typically built into the valve body) you haven't gained anything if fluid starvation is a problem.


 As large a trans cooler as can be accommodated might be a better route. It will increase fluid volume and since heat (breaking down he fluid properties) is typically a high cause of  transmission failure you get that added benefit as well.


Otherwise you probably need to find a junkyard that has a car with an existing C-3 pan and modify it yourself.