Yes they are generic.
The "trak-loc" plates onto which the caster slide and lock into have nothing to do with the caster itself.
The "release/lock buttons" the mandoismetal refers to is on the trak-loc plate not the caster.
I know of a place where you can get casters.
I just got to find it. When I do I'll let you know their website.
But you should be able to get them at a hardware store or Home Depot etc....
Just remove one of the trac-locks from your cab and bring it with you to make sure what they have is the right size and slides in/fits properly.