Well, I'll see what I can do, but right now I'm more focused on getting the other Lemmings music done first.
By the way, how's your searching?
I wasn't able to find any MIDIs for ONML, and I haven't received anything from "guest2" yet. Though at least you can count on DragonsLover eventually getting them done, if not already done.
Lemmings 2 I have more luck. I actually found some MIDIs I believe directly from the composer's website or something (but I no longer have the link to it, I chanced upon it thru Google, and it was quite a while ago). Unfortunately they were probably made for a specific, older MIDI card and doesn't sound too great on modern MIDI synthesizers. The percussion in particular were really messed up. I'm working on cleaning up the percussion (not my forte at all...) for the Sports Tribe theme (that MIDI sounded the best out of the ones I got from the site), then I can post it on my site and you can listen to it and decide whether it's worth including.
I'm also sure there's bound to be something in vgmusic.com for the Lemmings 2 music, I haven't even looked yet. And then as I said, I can rip music out of the ROMs for the SNES version of Lemmings 2, so MIDIs for that game shouldn't take too long to deal with. Come to think of it, I can also do this for the SNES version of Lemmings 1 in particular for the special graphics levels, although I actually didn't like the SNES version of those music quite as much as the PC version. Still, the effort is relatively minimal, and I guess there's no harm in having a diversity of options.