Finger Button Threads--Tuba/Euphonium Conn/King

[cheburashka]

I'm trying to undo the ravages of time on two horns--a King 2280 4-valve Euphonium and a Conn 90G trombonium. Each one has one incorrect valve button. I'd love to be able to find an x-mas tree button in silver for the Conn, but I've had no luck so far.

It occurs to me that I could buy one set of four buttons for the King, put the three buttons from the King on the Conn (they are the same thread) kill two birds with one stone. The problem I'm running into is finding matched sets of silver buttons in King euphonium size. Would Conn tuba buttons (easy to find) fit a King euphonium? Is there a chart somewhere that lists the various threads for different horns?