Sorry I did not see your question earlier.
I have several double bells. Not all Conns.
I would look for cannibalization candidates, single bell or double to start.
A couple of my horns came through E-Bay in years past.
I have not been watching E-Bay in recent months.
The first valve probably matches Conn single bell 1st valves of the era.
5th valve gets tougher because it probably is unique to double bells.
Depending on cash available may have to have a valve custom made.
That may cost more than a reasonably intact horn.
I would also start contacting the better known lower brass companies and see if their repair techs have any parts / cannibalization horn sources.
Good luck with the project.
Jim
Jim Babbitt
1960s 4 valve and 1971 3 valve Besson New Standards (Denis Wick 6BM) for regular playing
1936 Conn 5 valve 30I Double Bell (Bach 6-1/2AL) General Purpose Back -Up
1924 Buescher 5 valve (the Denis Wick is close) and 1940 Holton 5 valve (Bach 6-1/2AL) Double Bells for kicks.
1860s OTS Saxhorn when history is required (the Denis Wick fits)