S&W was selling 9mm Shield barrels, late 2012 and early 2013. They would even sell them directly to gun owners, through their store, and the price was $61 and $6.50 for shipping. I know as I inquired after buying a 9mm barrel for about $85, from a small distributor. The part number for the Shield 9mm barrel was 42199. Then S&W suddenly stopped selling them to individuals, stating they were a factory installed part only. I would bet they heard too many people asking for the 9mm "conversion barrel", which they never offered. S&W's position was that 9mm barrels should not be used in 40 S&W pistols, as conversion barrels. Occasionally the 9mm barrels would still show up at a distributor, through mid 2013. Since then it seems no one is selling them, as S&W is not releasing them to any distributors, who would sell them to the public.

I doubt the aftermarket barrel manufacturers are not making Shield barrels, due to patent issues. They could make minor changes to the design, to avoid the patent issue, if needed. The aftermarket manufacturers are still making barrels for the other M&P models. I would think the issue is they don't know if the demand for the 9mm Shield conversion barrels would justify the initial costs to design and manufacture the barrels. Conversion barrels are likely a very small percentage of their business.

Bob