I have a M & P 2.0 9mm compact 4" barrel. I cant find a recoil spring assembly anywhere other than the stainless steel type. I couldn't find them listed on the S & W web page. Would a Glock 19 recoil assembly work?

Try here

Smith & Wesson Recoil Guide Rod Assembly S&W M&P 9mm Luger 357 Sig 40

Smith & Wesson M&P M2.0 Compact Recoil Guide Rod Assembly: MGW

and here...look at the Questions...fits 2.0...Recoil Guide Rod Assembly : SMITH & WESSON RECOIL GUIDE ROD ASSEMBLY | Brownells

__________________
Loving retirement!

There are 3 barrel sizes for the M & P series, full size and the compact version in either 4" or 3.6". I dont think one size serves all. I'm looking for something for the 4" model

Well the link I posted says 2.0 but does not specify 4" or 3.6". Best bet is to call S&W CS and ask them. If yours is broken, they may send you a new one free.