I feel your pain... the older, sub commander size 1911's have some odd features, parts and such that are not or are minimally supported these days.
I have 2 officers model Colts with the aftermarket King's guide rod set up except the springs for it are now also hard to find to nonexistent. The Wilson 24 pound flat wire spring SEEMS to work in this application per multiple sources and my own trials but I am only at about 800 rounds so I would not consider that a statement of certainty in an absolute form.
Wolff springs for all my Colt needs. Mustang , Defender , Officer, Commander or Government. That's where I go first.
My Colt Officer is 1995 Its one of my favorite carry pistols and the factory recoil plug set up still working fine. I think that was a over hyped problem. That made some people a lot of money.
I buy my springs where most of the manufacturers get theirs, Wolff Spring.
If a gun has a spring, you can most likely get it from them. And their prices are very reasonable. I always have extra recoil and firing pin springs in my range bag.
Brownells had the complete inner assemblies a couple month ago and I have been able to order springs from them after Colt shut down selling parts on their website. Haven't tried the little Kimpie spring assemblies yet. That might be interesting.
My Colt Officer is 1995 Its one of my favorite carry pistols and the factory recoil plug set up still working fine. I think that was a over hyped problem. That made some people a lot of money.
I used to say the same thing until my factory 1985 retaining assembly launched itself down range. There was no warning. I never even found the plunger tube.
I installed the Wilson full length guide rod/reverse plug setup and never looked back. It was simple to convert, and the pistol was easier to disassemble and reassemble. The slide cycled a lot more smoothly after that too - I was never impressed with the crunchiness of the slide operation. My opinion is that the Wilson setup is a great improvement (as in leaps and bounds) over the old setup, which is probably why Colt currently uses a similar system. For $37 plus shipping, I never have to worry about it failing like that again.