Water Hammer is just a type of Accumulator Tank or Anti-Surge Accumulator.
Aquamist do a 30cc one for about ?35, and a 100cc for about ?45 not sure how they work on Shurflo pumps although I suspect it's more to do with the overall throughput of the system so 30cc is probably fine.
http://www.aquamist.co.uk/sl/plist/p...0/806-410.html
Larger ones (~2 Litre) for marine use are about ?30 also.
Andrew...