Anyone ever take a 40 C and convert it to 9mm? Is it just the barrel and mags?

As long as it works the same as it does with the full size models then yes. I've heard from a few guys that they have used the .40 cal mags but that the last round doesn't feed.

I've been searching for a way to purchase the factory S&W 9mm barrel, but cant find it anywhere. From what I understand, it should drop right in and convert. I'm not crazy about the Storm Lake only because the chrome barrel looks cheap to me. But that's just my .02

Can anybody tell me where I can find a factory replacement 9mm 3.5" barrel?

I have a .40 to 9mm in stainless. I use 9mm magazines. My base frame and slide is a .40c.
When considering the purchase I called Storm Lake. They confirmed it is a "drop-in" conversion.
They actually call it a "conversion" from .40 or 357 SIG to 9mm.

Check out this thread. It certainly appears to be possible based on these comments. In fact, it even sound like you don't actually need to use 9mm mags.

Questions about conversion barrel

Good luck finding a factory 9mm barrel. NOBODY has any in stock.

I ordered mine from midway. Well back ordered. It should be in stock mid-late march. Until then I'm perfectly happy with my .40c.

Same here, ordered from Midway and expecting it in late March. Went ahead and got 2 9mm mags to go with the conversion. Hope all is good.

Same here.

I picked up three 9mm mags. Now I have to ask talon grips for three finger rest pieces haha.

I cant imagine not being able to order direct from S&W. Im going to try and call them tomorrow.

Storm Lake conversion barrel is awesome! Best accessory yet for my 40c. My groups are tighter with it than my factory 40.