Hey I've recently bought a sd40 and I like the pistol i just would like a higher quality recoil spring assembly and metal trigger, would the assembly out of an m&s or a glock fit? If so where's the best place to find one?

Wolff Gunspring Makers
http://www.gunsprings.com

No, the RSA from Glocks and M&Ps won't interchange.

Galloway Precision makes a stainless steel recoil spring assembly. I recommend them.

I put the Wolff spring in my sd40ve, the spring and rod are steel. Stayed with original weight, not much difference in recoil that I noticed. Kept the original as a backup.

This^^^^

Galloway Precision :: Smith & Wesson Performance :: Sigma and SD Performance Parts :: Assembled Stainless Steel Guide Rod for Sigma/SD-VE Pistols