You might try Armslist.

Mossberg 500

find a used 870

My first shotgun was a Remington 870 combo. Came with a shot barrel and a slug barrel in the same box. That was at least 15 years ago. The stock is a little beat up and I don't use the shot barrel much anymore, but it still puts deer down every year.

Shop all the area gun shops, and even pawn shops if you don't care you may be buying a stolen gun.
Check for gun shows in the area too.

:D Al

If you still haven't purchased a gun, go to a local hunting outlet store and get lined up for a hunters safety course. This close to season they will fill up fast. The instructors there are usually pretty knowledgeable and can direct you to a local location to purchase a firearm. Safety is paramount, then the fun begins; don't be a statistic and good luck.

Check out new pump actions, and give them a good shake. You'll get a feel for what should be a little loose. This will give you a comparison when inspecting used guns.

When looking at used guns...
Check the bore of any used gun you're considering, and look down the outside of the barrel. If you see any warps or bulges (easier looking at light reflected off the metal) forward of the chamber and behind the threaded area of the muzzle DO NOT BUY at any price.

Cycle the action. You should not encounter much resistance opening or closing the action. The bolt should lock up tight, but not require excessive force to "shuck" the shell. The safety should snap into place too.

Remove the magazine cap and take out the spring and follower. The inside of the mag tube may look dusty, but should not be rusty.

Check stock and fore-end for cracks. Small dings and nicks in the wood are "handling marks" and insignificant.

For all around use, look for a gun chambered for 3" shells and a 26" or 28" barrel.

Good Luck, Good Shooting and Good Hunting!