Depends on how thick (diameter) the 'u' portion of your lock is. Master Lock has an old school bracket that's very well made and almost bulletproof, when compared to the other brackets that come with even the most expensive u-locks and seemingly break easily (the bracket, not the lock):
http://www.cambriabike.com/master+lock+parts.asp
Lots of alternatives out there, like Twofish lock blocks, mega block, etc. :
http://www.twofish.biz/bike.html
or you can make your own with leather or nylon straps with buckles or even velcro.