While not always listed as CPO, you can still find used (formerly LEO Agency) SIGs on sites like CDNN, AIM Surplus, and, as mentioned, Recoil Gunworks. Probably elsewhere as well.

My first CPO was a 220st that looked new. It was in the early 2000’s but I think I only gave $525 for it. It’s one of my favorite guns. The CPO program is something that I really liked from Sig.

I picked up an all German 228 CPO at the Experience Center today. Guy who waited on me said they were cleaning out old inventory at the factory.

Here's the Recoil CPO section GW CPO page

SIG CPO stopped when SIG quit caring about making the world's greatest firearms. They knew their product could still be stood behind, even after they were used.

The last time I picked up a CPO gun was well over 15 years ago. It was a P226 9mm Sport Stock.

My first was a P225 I bought from a distinguished forum member in NW Houston some years back. Still one of my favorites.

I've seen used Sig P226's both DA/SA and DAK at GT Distributors in Dallas. They were all well worn, with the two DA/SA guns made in '88 and '90 respectively. These were hardly CPO's, but would have made a nice restoration project.