Almost every gun shop worth its salt should have a slug barrel for the remington model 870,if not then they should be able to order one with no problem.
Check with Remington thru customer service at their website, and see who is a distributor in your area.
Yes
You shoot at what is called a "patterning board" to determine the shot density at different distances (assuming that you are shooting shot and not slug). Your best bet is to buy a book. Check out Amazon.com or DBI books.
Remington 870 stocks can be purchased from a variety of places such as Cheaper Than Dirt, ATI Gun Stocks, eBay, Brownells, Midway USA, SCHEELS, and Bass Pro.
Find an authorized Remington Repair center. You can find a list on Remington's web site.
in my area u can buy a new one for around $325
This should be a Mossberg 500 in a Montgomery Wards suit. Check any dealer for the availability of a slug barrel.
no you cannot. sabot slugs are made for rifled barrels. I would buy a rifled slug barrel.
It doesn't look like there are much out there.
Will be hard to find, and expensive. Do an internet search for Corson's Barrels.
Try egunparts.com, gun shop, gun show, pawn shop
Browning did not offer one, but you may find an aftermarket Hastings barrel (www.hastingsbarrels.com) that will do the trick.