if it's just a u-bolt clamp or an olive clamp, you could probably pick one up for a couple of quid from Kwikfit/etc
if you're feeling flush and the exhaust's a sleeve fit, could be worth using a Norma/Mikalor type clamp, which are more effective
by the way, if you've an exhaust supplier who deals with Bosal local to you (lots do), their part number for the alloy bracket thing is 255151