Speak with your local ECB development officer -they'll be based at the closest county cricket club - or let me know where you are and I can send contact details in a PM. A lot of their work is based around increased participation, schools and clubs, but they will be able to advise.
I would also look at local schools - a constant influx of potential players year on year, at all age groups. It means clubs getting out and liaising with schools and embedding school-community club links. Player pathways and the new, young players become the lifeblood of any club.
In terms of leagues, they need to understand that their lack of development focus is killing the game at a local level. If a number of clubs are able to approach them at a league meeting, highlighting their concerns, possibly with the support of the local cricket development officer, hopefully it can move forward.
The ECB are big on developing Last man Stands, which may be an option in addition to T20...