Few Folders are double-edged, as carrying them safely is a serious concern.
The MOD doesn't come double-edged, but the false edge is still hidden inside the handle when folded, so it can *theoretically* be sharpened, if only for a limited length. Same goes for the SOG Pentagon Elite Series, the Benchmade Pardue-530, or the Gerber Applegate-Fairbarn. Any folder with a double-ground blade that fits entirely within the handle - or at least partially enough as to provide shelter for the potential second edge - can be altered in this way. I had such a knife for a while, a Pentagon Elite, but these days, I don't recommend it. First off, if you ever use that second edge, you'll be working against the locking mechanism on the knife, increasing not only stress and wear, but also the odds of a catastrophic failure. Second, it makes the knife doubly dangerous if it ever opens by accident. Lastly, since a double-edged knife almost always spells
weapon, they tend to attract more attention from the cops, reasonable or not.
If you are serious about a double edged folder, there are only two options I could suggest. Don't get a conventional folder, or alter one, with two edges. It just isn't safe. The first suggestion would be a balisong, or butterfly knife - their construction makes them safe enough to mount double-edged blades. Benchmade makes the best.
However, if the balis are illegal in your area - which they almost certainly are - then there does happen to be a convenient loophole knife:
http://www.coldsteel.com/tripleactions.html
These knives aren't technically balisongs, and can be found in a number of places. I've handled one of the dagger versions in Canada before. Notwithstanding, they're still safe, reliable, and double-edged, like you wanted, though I would suggest attaching some rubber or G10 if you have the know-how.
PS - Cold Steel also manufactures a number of bowie knives, as well, most of which have a sharpened false edge, like you were after:
http://www.coldsteel.com/16cc.html
http://www.coldsteel.com/16absj.html
http://www.coldsteel.com/39llb.html
http://www.coldsteel.com/fixed-blades-trail-master-series.html - no double edge on this last one, but it does have a cantled (convex) edge, so it cuts like magic.