I replaced my plastic cable guide under the BB shell with one the LBS had, since the cables had worn some bad grooves in it. The old one is quite a bit larger. The new one also seems to be a smaller curvature than the shell, but when I tightened the bolt it flexed into place. Where/how can I get one that matches this. OE one?

eBay is one place. Also try your local bike shops. Shouldn't be hard to find at all.

Size shouldn't matter as long as the FD cable clears. The Rd cable leaves at a tangent off the bottom of the shell, so it's never a problem. Even if the FD wire rubs the back of the BB shell between the chainstays, that too, is OK If you're concerned, a bit of protective tape will prevent any damage to the paint.

I tell you this to open up your options. There are nice steel guide available at reasonable prices, and they'll outlast your frame.

All pretty much the same.
The bigger one looks like this campy:
https://www.universalcycles.com/shop...009&category=7
Smaller Shimano?
https://www.universalcycles.com/shop...695&category=7

Yeah the one I got from the LBS is that exact Shimano blue one.

I doubt my original one is the Campy one. My Felt bike came with FSA/105-5700 gruppo.

seek out Felt spare parts then..

Felt sells the guide as part of a small parts kit that costs anywhere from $15 to $50, but not for my 2011 Z frame.

Going back to the original issue of the new guide being skimpy (for lack of better word).

You might try a small patch of muffler or teflon tape cut to shape and mounted under the bolt on guide. The plastic guide will keep it in place and do most of the work, while the tape will extend the protection to where the cable leaves the shell.

A few cents and a few minutes work and you're on your way.

I don't know, it will probably be fine. The cables don't touch the frame at any point, even with the smaller guide.

Sounds like it works, and think of the weight you saved...