Hmmm...
Some fun ideas for the M-1 carbine vias-a-vis magazines (though admittedly difficult, sacrilegous, fanciful and/or odd):
1) Get some Automag III magazines (8-round pistol magazines) from the new High-Standard company. They are set for .30-carbine, so that gives you 3 more rounds per magazine, as opposed to the "pinned" ones. The tricky part may be to configure an M-1 to take them.
Additional point: If you could find an "Iver Johnson Enforcer pistol" magazine, that too might be fun...but in reality, be aware that mag-well modifications, etc., etc....
2) Re-chamber the M-1 for another pistol-calibre cartridge and get it to feed off of 10-round pistol magazines. Some "hot" ideas (though not necessarily 10-rounders) include the 7.62x25mm TT cartridge, the .460 Rowland (which does come in pistol magazines), and even the .45 Winchester Magnum (see:
http://www.theothersideofkim.com/index.php/ggps/6176/).
Just some food for thought...
P.S. While I do read Kim's website every now and then, I am in no way endorsing all of his views, etc., etc., sheesh...