Biker is right about finding .357 Sig. It's usually around. On another note - sure, the guns from which it is fired aren't very popular, which in turn makes the round itself not too popular - or vice-versa; but as a result it usually stays on the shelf longer for you to go grab than 9mm does. Back to what Biker was saying: +1 on barrel/caliber/mag interchangeablility as well for the Glock platform. It's a modular design. The Sig P250 didn't start it. I'm not knocking Sig though.
Southpaw speaks the truth as well. All good points. In sticking with what he said about picking a gun that feels well and fits right for you, why not go back to the compact Glock (G19,G23,G32) that you're already comfortable with? Those guns may be all different calibers, but frame-wise they're nearly identical. You seem to want something different than 9mm, so that leaves you two more choices in the same size range for the Glocks. Sounds like you're trying to keep an open-mind for everything, which is awesome, but don't forget about what has worked best for you in the past. I myself can't wait to pick up my G32 .357 Sig - it's the same size as your old G19.
Let us know what you end up doing man!