I had the same problem, but given the 'cheap and cheerful' nature of this beast I I didn't even bother trying to get 'spares' – I just took one of the existing sets out to copy. The set is just an odd shaped plastic arm and a spring so I made a close copy from a couple of bits of thick plastic card and a spring I had in my bits and bobs. I say close copy because the only spring I had was a little long, even when worked over to get the right sort of tension, so I had to make the place where it hooked onto the arm higher up. Works fine though.
Access is easy – just remove the four screws at the rear of the tx and the back comes off (though still connected by a few wires) revealing all the mechanisms for the levers.
Edited By Michael Sheridan on 09/07/2013 17:09:37