I have been looking and can't seem to find the felt to go between the manual and piston rails. Can anyone direct me to a possible source. Really would like black if possible.
I have had success with the following self-adhesive felt from Amazon at https://www.amazon.com/gp/product/B076P51CHW/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 for the same application you have mentioned (as well as a lot of other places.) I was concerned about whether or not the adhesive would last, but some parts in my organ have had this felt in use for years with no indication of failure.
I purchased the following from Howard Piano that is on the bottom of the piston rails between manuals. I'm not sure exactly where you want to install felt. (I also purchase other felt since I rebuilt the 1960s Rogers keboards): Felt, red 5/8" wide .058" thick (1/16") x 25 Ft Long.
Check out a piano materials supplier in your local area. Alternatively, contact a local pipe organ builder and ask where they source their materials. The item you are looking for is called "nameboard felt".
Glad I could help. Years ago I restored reed organs. I often went to piano suppliers for materials, and nameboard felt was usually on the shopping list.