I have a pouch or holster for my extra mags that I got at Walmart. I paid about $9.00 ea. for them and it is black nylon, just like most of the ones on the market. I has serve me well and have no reason to purchase any other that will cost more and not do anything for me. They also have a double mag holder online, but I have not seen it in my local store. I just use 2 singles. Some prefer leather, but I don't see the benefit or difference it makes.
I'm good with the Wally World Special. Comes in single or double pouch. Great price on these Bulldog pouches.