Some google digging yielded this.
NCStar
I don't know what the quality of this product is, but I found a forum post where the guy said he had one of these on a full size M&P and was looking for a holster.
Here is the company's site:
NCStar
Hopefully this is a start. Just google "rail mounted laser M&P" and see what comes up past this.
Good luck with your project!