Since Robinsons of Stockport stopped brewing their two milds last year, Hydes have taken over sponsorship of the event. Hydes brew three milds: the light 1863, mid-brown Mild and dark Old Indie.
Two things have become clear on the way round a dozen pubs:
1. Your best chance of finding a pub selling mild is one tied to a regional family brewery, which in Manchester means Holt's and Hydes (I'm not sure about the availability of mild in those tied to the other independent in the Manchester area, J.W. Lees of Middleton).
2. For microbreweries, mild is a dark beer: the only light milds I've drunk have been from a regional brewery (Hydes) and a national one (Banks's).