Rear Air Ride Shocks - Z55 : any company rebuild these?

[Foggy]

As title states. Does anyone rebuild these (OE GM ones) ? Or pay as cores ??
These have gotten soooo expensive $$$$
And I absolutely don't want to get rid of the Z55 active suspension

 

[SpareParts]

Arnott buys cores and rebuilds. Only place i know of.