The only launchers that are available right now are the JCS nerf launchers. They shoot the nerf rockets and depending on game rules you can shoot bunkers and eliminate the players inside said bunker. They're also used for taking out tanks.
http://www.bp-usa.com/launchers.htm
There was a M203 style grenade launcher made by a company called Scepter but the company went under. That one actually fired paint grenades.
This one is supposed to be released soon, it's manufactured by a company called Metadyne. They make GOOD stuff. Aside from the paintball products they actually produce real firearm parts too. Here's a pic. This is designed as a front loading 2" nerf launcher.
Pictures are courtesy of Van Tenpenny www.andimages.net
They other styles are Airsoft grenade launchers. I'm sure with some modifications they could be used to fire Nerf rounds.
As for a "shotgun" that actually fires multiple paintballs, alot fields have rules against. Alot of places want one trigger pull and one shot. That doesn't happen all the time with ramping modes and all but; what are you gonna do!
I'd had seen a marker or two out there that shot sabbot rounds for the shotgun effect but they wanted $$$$$$$$$$ for them. I doubt they sold many for the price they were asking.
Hope that helped some!
