I wrote up my how-to-make for a tool to do the necessary, on madmodder.net search for 'stuck collet chuck arbor' post 78 has a couple of drawings. I suggested milling the parts, but in a pinch hacksaw and file or angle grinder should do?
On my lathe the screw for the tailstock runs down so that it will push on the tang and pop it out when you retract it fully (with the keyway to prevent it from turning).
Is there not a similar thing here where you can stick a bolt down the centre and press it out that way?