They have plenty at the stores. If it's just the lanyard and pouch you want, not a trading-starter-set with pins and lanyard, you'll probably find the pouches to be around 5+, and the lanyards around the same. Not dirt cheap, but not hideous either.
Now those are the clear pouches with a character like Tinkerbell, or the skull and crossbones, etc, on it, with a ziptop. And the lanyard styles vary quite a bit!
You can check on disneyshopping, though. I bought myself and DH the cutest lanyards (with a medallion thing that I would never wear on the lanyard, but it looks good when your'e just holding it to look at) that I'd never seen in the parks...mine is a bright aqua blue with a retro Mickey theme, and hubby's is a grey Nightmare Before Christmas theme. Got those 2 Yuletimes ago.
There are also interesting attached lanyard/pouch with proper zipper (not ziptop) sold in various stores. I think some have found them at the resort stores, but I know I saw them for sale in the Millie's Restaurant giftshop. Cute themes like Cars, etc, and they might be better for kids b/c of the "real" zipper.