There are four bike shops in Manchester:

The Bike Barn on South Commercial street.

The Alternative Bike Shop on Mast road.

Jakes Bike Shop on Kelley street.

Concord has Revolution Cycles and Eastern Mountain Sports, which I have read on other forums that say it has a good bike department.

Here is a link with some info:

http://forums.mtbr.com/showthread.php?t=383576