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
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.