Michael Wright did a very interesting series of workshops on the Jews harp at the last Whitby festival. I hope they'll be repeated, but I don't know for sure. His brother is a virtuoso player if you want to look for CDs.
Plenty of information on the internet about the Jews harp. There is a worthwhile journal published in the USA. Largely died out in England, but time for a revival perhaps. Still going strong in countries where traditions are more valued.
Hard to buy a decent instrument in England, but you can order on the net. Norway produces high quality instruments, but at high prices. I'm not suggesting they're not worth it, but try German instruments at more affordable prices. Give some thought to the key if you want to play in a session.