Those might be hard to find for free......
Are you referring to the programs or the mid files?
I'll address both.
1) You are not likely to find the latest underground freestyle from a basement, but you will usually find the latest Jay-z or any other pop type rapper if you search the midi sites. Most of these files will suck, but will most likely contain basic melodies the original poster is seeking even in the bad arrangements. The range and quality expand if you purchase commercial midi files.
2) Since he did not mention budget, I'm not sure if he is looking for freeware. I presented commercial software as one option. Like all things, you get what you pay for, so expensive programs like Finale are going to give him more options, probably a lot more than what he needs. Not encouraging the illegale route, but I am sure most people know, Finale or Sibelius can be downloaded from various sources. As for free resources, none will give you the same control as the more expensive options, but free sequencing software like computer muzys which comes free with computer music magazine will at least show the notes in a piano roll. Even a functional demo like fruityloops, will show the notes in a piano roll if you import a midi file. not the best way, especially if you are used to reading sheet music, but still an option.