good morning gents.....I just picked up a used gen 1 full size M&P and had a few questions. It had internal trigger work done on it by the good folks over at ATEI, but it still wears the curved hinged trigger. I'm satisfied with the internal work and trigger pull, but wanted a flat trigger shoe. What's my best option for just a flat trigger shoe without buying an entire trigger kit?

I think you can buy just a flat trigger shoe from APEX

Unfortunately, flat-faced M&P triggers aren't sold as stand-alone triggers.
You can buy the curved action enhancement trigger by itself, but not the flat one.