You can always buy it off the shelf like you did with the Glock 17.
I would get an American made frame with the new larger extractor just to take it all the way to the extreme. Since many of the Sig collectors think those are the end of the world.
You know only recently has my arsenal of M&Ps start to rival my collection of Sigs, I bought quite a few of them over the few years I was shooting Sigs. Though I am still a couple of years away from reaching the round count I have with Sigs I didn't keep records those early years but based on what I had the final couple of years I probably have around 50k through the main Sigs.
My favorite is still this fella right here:
It doesn't look nearly as good now, as there is an almost permanent stain of gun powder on the front inch of the slide. You know I should probably pull her out to make sure she is still in good condition.