North Texas? Whereabouts? Cabela's north of Fort Worth had an aisle full of Knoxx stocks, Speed Feed stocks, side saddle carriers, and other 870 accessories.
Search Brownell's online catalog for 870 parts of all kinds.
If you ever hit the gun shows in the DFW area there are a couple dealers who have shotgun accessories. Bladerunner is a knife dealer who sells nice knives on one side of their aisle, and on the other side they sell AR and gun accessories including Surefire lights and their prices on Surefire Shotgun tactical light forends is pretty good. There is also a gun dealer, and I can't remember their name, who deals in tactical shotguns from Remington and Mossberg. He has all sorts of stocks, forends, side saddles, etc that he will install on shotguns he sells. I bet he sells the accessories separately also.