In Ireland, I'd put the figure at around a hundred active volunteers running RPSI trains on the mainline, DCDR, Stradbally, Waterford and Suir Valley. Equally grim are the number of enthusiasts who are very vocal about what should be done, yet have a myriad of excuses as to why they can't help do it. The Irish Traction Group, which preserves and operates a number of diesels, was started by some English enthusiasts, such was the lack of interest locally. Any time one of our volunteers (we have 200 members and 26 active volunteers) visits an English heritage railway, they always return envious; some of the larger outfits have close on 1000 volunteers and numerous paid staff.
Mods, perhaps this thread should be moved to Prototype Talk?