I've found
http://www.joinmyband.co.uk and
http://sheffield.gumtree.com to be really good for forming bands, as they're both totally free! With the massive influx of students there, I'm sure you'll find something pretty soon, as everybody knows the first thing to do after Fresher's Week is to form a band. As for music shops, I'm not sure there, but try and find guys like MAMMOTHvolume and PM them, they're pretty ensconced in the Sheffield scene
AFAIK. Every time I've played in Sheffield it's been absolutely awesome, it's a great town, and there's been some great bands from around there, like The Miramar Disaster (RIP).
I'm in Barnsley next week recording, I'll ask the guy there if he knows of anyone for you, how's that? Good luck fella...