Supply seems to have dried up recently, there used to regularly be ones on ebay, but not for a while. If you can get a Simpsons one thats your best bet as they have been dried store since new, they claimed only to have one left and wanted 4k plus, but it sounds as if they have more than that. Lots of the other ones out there have been in damp garages and tend to be rusty.

I might be selling one of mine in the near future, all depends on another car I am after. I will drop you a pm if I do sell