Gun Parts subcontracts directly with Triple K for aftermarket magazines.
If you see the word "Replacement" in the catalog it means they are Triple K magazines.
Gun Parts usually has some original magazines on hand for most guns.
They are of course used and priced higher than aftermarket.
I personally always request original magazines when ordering them from Gun Parts.
As the other posters have stated, original Model M magazines are not terribly rare and you should locate some with a bit of searching.
There are three basic styles and if you aren't looking for 'correct as issued', try to buy the later magazines.
These are better overall in quality and less prone to cracking than the early magazines.
You can identify late magazines by the two dimples on the bottom sides that hold the floorplate in place.
These magazine also have an even blue finish.
Earlier magazines have a two tone finish, lighter in color at the top of the magazine around the feed lip area.
$30.-- to $40.00 used average and $50.00-$75.00 for very good to like new.
New in package magazines run $90.00 to $125.00
.32 acp magazines, for some reason, are generally less expensive than .380 magazines even though there were more .380s made than .32s.