Rob,
eBay is a decent bet for these switches. I finally picked one up after having my Beta Lead for about six months (same switch). There are two versions, one that just does the channels and one that does reverb as well. If you're very handy with electronics, the service manual is in the museum, you could try to build your own if you could replace the connector.
Price varies, I lucked out and got mine for about $75 with shipping - I've seen them go for $150+ though!