Well, I just replaced the air pump on my 2000 Blazer, and at the same time while diagnosing it, I seen that the air solenoid valve...
was bad. Ok, search online for a replacement. Nobody lists anything for this part. I think I may have found the original part #, AC214615, but that is no longer sold. Even AC Delco'* website no longer shows a listing for it.
I stumbled upon another part similar to this one, Duralast/Canister Purge Valve Solenoid PV164. Which is IDENTICAL to the one needed for the secondary air system. This one costs $38 at Autozone.
But wait! My 97 Bonneville has something similar!
Duralast/Canister Purge Valve Solenoid PV137
And this one only costs $23. Almost a $15 difference because of a bracket.
So, being the experimental and cheapo that I am, I opted for the $23 version. One .003 cent zip tie later and I was back in business with a fully operational secondary air system.