There is a market for used weapons, the internet is a good place to start.
First take a look at the main page of the forum, under THE MARKETPLACE.
There are usually several firearms for sale there.
As for buying new guns, the two main vendors that people speak highly of on here are:
Larry Kneesk @ knesekguns.com
Lin Schyver @ schryvergunsales.com
Both of these dealers offfer package prices with all the accessories. I think it is usually better to buy a package deal, as the price is usually better and you don’t have to worry later on about getting the right accessories.
I hope this answers your questions, but if not, or you have others, don't hesitate to post them.
People think I'm paranoid because I own guns.
If I own guns, what do I have to be paranoid about?
Calling an illegal alien an "undocumented immigrant"
is like calling a drug dealer an "unlicensed pharmacist ".