Footswitch, I'm not sure. IIRC, the C30 uses just a plain latching switch (check the manual to be sure). If the Marshall switch is latching it can work (or worst case, be made to work).
Valves, I'm not sure what shops you have your way, but you can always get from Mr Valve:
http://www.mrvalve.co.za/. If you want to make sure it's the valve rattling, simply swap your 12AX7s around and see where the rattle goes.