Z's are pretty rare to come up, and as pointed out, they go quickly. https://www.johnfoxbass.com/dingwall Keep an eye here, or reach out to John and ask to be contacted if he gets a Z in.
You can also scour Reverb, but again, pretty rare to pop up there too.
I'm about to get my 2nd Z. That'll bring my Dingwall collection up to 6. Definitely a good choice. The Afterburners are also solid Dingwalls, but the neck on the Zs and Primas are just above and beyond.