I have a similar holster, but it's camo and has a clip in the back. Can't remember where or when I got it, probably 10 years ago. It works well enough, though it came unclipped one day last year when I was taking my shotgul sling off my shoulder.
Far as refills go, I take a refillable disposable lighter, then cut the valve out of the bottom & grind it to 1/4" diameter. Next, I drill a 1/4 inch hole in the center of the bottom of a spent ThermaCell cartridge, then epoxy the valve in the bottom. Once the epoxy sets, I can refill cartridges with bulk butane cans for recharging refillable lighters. I haven't bought butane refills for my ThermaCell in 5+ years. Insecticide mats can be bought a couple dozen at a time off eBay.
Jim