Depends on the parts.
Numrich/Gun Parts Corp has everything to build a new 15-22 except the lower receiver. But not everything is in stock.
Midwest Gun Works has many S&W made parts. Some that also aren't in stock.
Several companies make their own 3rd party parts like barrels, handguards, charging handles, and extractors. See Volquartsen, Tandemkross, NDZ Performance, Tacticool and Taccom3g. Probably more that I don't remember right off or haven't encountered.
Several parts are interchangeable with an AR-15. Pistol grip, stock, sights, magazine release, and trigger can use anything made for an AR.