You may have trouble finding .38 Super ammunition, while .45 ACP is available in grocery stores and news stands all across the nation.
I hear that .38 Super is big in Mexico, though.
The .38 Super is a high-velocity round that was designed in (I believe) the 1930s, to go through automobile windshields. It was meant for use by highway-patrol and other police officers.
As I have written elsewhere, the ballistics of the cartridge aren't important unless the delivery system (that is, you) can place each and every shot accurately and effectively, in which case almost any round will suffice if you understand its limitations.
The reason that .38 Super 1911s are "popping up" may be that their owners are dissatisfied with some aspect of the gun's performance. High-velocity cartridges are hard to control, and to deliver accurate fire with.