The only way I know is to contact Hohner and request valves ("wind
savers") for one of their chromatics. They will sell you a large
collection for not much money. A guy named Bill Rommel used to sell
self-adhering valves, but he died earlier this year and I think it
unlikely that his family is continuing his work. You may inquire at
http://www.harmonica-workshop.com/
Good luck,
-LM