It's not midi actually. They were mostly mod files, and some were written for chips like the NES. Here is a link to the one of the stage music mod files. This is the actual mod itself, and to play it, you will need something like VLC, or Foobar2000 with the Dumb Module Decoder plugin. If you use the ladder, uncheck use Playpmod or Modplay in the plugin's preferences to get the proper affect. About midi, hmm. If you really were desperate, there are probably 8-bit soundfonts around, however I don't recommend you use them, as the emulation is generally not very good. The chips used often respond in certain ways that just can't be replicated with midi.