I ran into a fellow at a local range the other day who was running a lot of rounds through his Glock. He was using a mag loader like this one:
Each time he needed it, he dug into his pocket to fish it out. When he walked back to his pickup, I noticed an otherwise squared away MOLLE-type rig on the tailgate set up for M-4/M-16 magazines and his Glock large frame semi-auto. I asked him if he had a pouch to put his speed loader in and he looked embarrassed when he answered no, he hadn't thought about it. I told him that GIs using M-3 grease guns in WWII and Korea would have their mag loaders clipped onto their web gear by the simple expedient of unhooking one of the front straps from the belt and threading the mag loader through it. It rattled a bit against the snap hook, but it was handy.
I've seen photos of French paras doing the same thing with mag loaders for their SMGs in Indochina and Algeria, both M-3 grease guns and MAT-49s.
M-3 Grease gun magazine loader.
I suggested to the young man that from my own experience, an M-3 mag loader fit very nicely into a current issue single MOLLE 40mm grenade pouch like this one:
I told him I was certain he could rig one up to his combat fighting vest for his Glock and it would fit just fine and he wouldn't have to dig for it. He thanked me for the tip.