Questions regarding Kalison valve section screws...

[cjk]

Tuba Exchange carries G+P stuff. Call them and ask. They might have parts.

hornguys.com lists a G+P cimbasso. Maybe they can order parts.

If you have one of these tubas, you should be able to take one of the screws to a hardware store (even Home Depot or Lowes), they should be able to measure the threads and tell you what size it is.

If you have a $15 pair of calipers, something similar to this might help you:
http://www.wikihow.com/Read-a-Screw-Thread-Callout" target="_blank