I think you will be lucky to find some. I have over the course of about 3 years managed to find 2 sets but they weren't cheap (£90 ish if memory serves). I have totes with the idea of using the cartridges from some rst XMO forks as they may fit, but I think the XMO fork was better than a judy anyway so kind of pointless.
I could let a set of my Englund ones go for the right price.
I got a set of Englunds fitted in some Judy SL's off ebay. Keep a eye on the bay and you might find some. Mine were from America and the forks were crap but the air carts were spot on.