Since you'll have to find a retailer who stocks supplies, your best bet is to speak to them about plant & fish selection. Some tips, though:
1) If you live where the ground freezes, you either need a pond deep enough to NOT freeze, at least in a small area of the pond. Goldfish will usually survive a winter if the pond is deep enough. Otherwise, you need to plan for an indoor aquarium for wintering over the fish.
2) If you've ever heard of racoons visiting your neighborhood, you can expect them to visit the pond and make off with plants & fish.occasionally. You won't want to spoil the look of the pond by keeping a framed wire screen over it every night, but it's a good idea to have one ready, in case the 'coons find you. They'll usually move on once their dinner has been made difficult.
3) If you don't like the shape (or depth) of the ready-made hard plastic pond liners, find a dealer who sells thick rubber sheet for lining ponds. It's tough as leather, and usually sold by the foot.
Anyway...find a local dealer.