All the ones I could think of have been mentioned.
I seem to recall Iron Horse died in 2008/9 victim of the credit crunch, as far as I remember they sold the Sunday that was THE DH to have at the time thanks to Sam Hill but I couldn’t name another one of their bikes, I doubt you can make a successful bike co from DH sales alone.
Cove are all but dead sadly, down to 4 frames, a Hummer which is there’s, the Hustler which is an off-the-shelf Chinese frame with a few Cove bits (or was that the old one) the Shocker the which isn’t massively different to the one I bought 10 years ago and wasn’t new then and the G-Spot which is 8 years old – can’t imagine they’re still making 26” wheeled Enduro and DH bikes, they’ve just been sat on the shelf for a very, very long time.
I wasn’t aware Klein were dead, I only ever saw their crazy airbrushed frames ridden by old beardy guys, assumed they still made them on the quiet and you’d only see them leaning against a beer garden bench surrounded by pints of real ale.