Check ebay for a M32.5 x 0.5 ring. B&H has them listed. Also, if you can't find one SK Grimes can make one (but they may have some in stock).
Check ebay for a lensboad with a 32.5 or 25mm opening. If you get the smaller opening it can be enlarged.
If you want to mount that lens on the lensboard with the 50mm hole you will need to have SK Grimes make you a flange wide enough to bolt onto that lensboard and cover the hole.
The threaded 39mm lensboards seem poplular on ebay now. So, an alternative is to get the 39mm threaded lensboard and a lens with 39mm threads. Lenses are pretty inexpensive these days.
Or, B&H has a M32.5 to M39 step up ring for enlaring lenses to allow you to use the more popular 39mm threaded lensboard (since the M32.5 lensboard may be hard to find).