If you have an aquarium club around and can attend monthly meetings (or as often as possible). You may find some local breeders, and have a good chance of getting some nice fish.
Are you planning on continuing as a fishless cycle?
If you want to gain a good amount of basic fish keeping info, check out the link in my signature, "Getting Started" is a Aquarium Advice article.
Realize that a female Guppy is nearly always pregnant and this will mean you might require an additional tank with great filtration for fry. Hikari First Bites is a good basic food for fry.