I just keep a look out on eBay for them, they are not cheap new ( £200 plus) but on eBay I think the most I have paid is about £60.
One thing I will say when building a panel is it is important to have the keyboard angled and the MPG low down on the panel as if you dont then it gets tiring very quickly when using them. The big lathes MPG looks high up but its actually not too bad as the panel sits quite low, it would however still have been better if it could have been at the side of the keyboard, sadly that one is too big for that. When I did my first machine, a Bridgeport I had the MPG on the side of the head, your arms ached after a few mins if using the MPG so I have made sure I dont make that mistake again.
Hood