There's a pdf here with measurements etc. & some other ones that members have made themselves: https://www.prospectingaustralia.com/forum/viewtopic.php?id=10228&p=1
Maybe you could do up a rough sketch of what you want/sizes from there & get a local fabrication shop to knock one up for you. I doubt they would charge too much as it would be a pretty basic build for them.
A lot of fabrication places can make this gear cheaper than you can buy it even used. They're always worth a chat if your not wanting to build something yourself & it's difficult to find.
Well that got me interested .... never heard of it before and while it's most likely the domain of gemstone prospectors I have no doubt it could was gravel in areas where water was scarce to pan/sluice off later.
Thanks for that bit of knowledge.
Cheers T.