While I often recommend a DIY approach in circumstances like this, in this case I strongly recommend that you take it to a competent technician and have it evaluated and fixed. Even if you could find exactly the correct original parts, it's quite possible that (even if you install them absolutely correctly), your valves will be out of alignment because of valve wear.
You CAN measure and confirm the correct alignment of your valves, and you CAN (on the basis of measurement) buy a set of felts and bumpers that will correctly align the valves, but that process is somewhat complicated and requires a tool that you either buy or make.
In addition, for an instrument that old and of that vintage, you should have the valve guides checked to see if they need anything to insure correct alignment -- or if in fact they're sufficiently worn to require replacement.
I've actually done all of this on my own 1924 tuba and it came out great -- but it does take time to learn how to do it and then to do it with the required precision. Often, to get the correct vertical alignment you need one or more quite thin "shim" felts. A repair tech will have all of those since he does this sort of thing all the time. You, on the other hand, would spend a lot of money ordering, and then trying, several before you got it right. You'd likely spend more -- and suffer a high degree of frustration while doing it -- than you would by paying a competent tech to do it.
He should first test the instrument for leaks so that he can include fixing any in his estimate. There may or may not be any -- there aren't in my 1924 horn except for a very mild leak through the third valve that I'm ignoring since it doesn't matter.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)