Changing a plug is hardly rocket science. All you need is a small screwdriver and a sharp knife.
Go to any DIY store and buy a normal 3 pin plug. (Wilkinson's sell them for under a pound). However, look for a label which states that the plug has a 3 amp fuse. (That assumes that it's a normal domestic hi-fi amplifier. If you've got a concert amplifier with an output of over 500W look for a plug with a 5A fuse. In the unlikely event that you've got a massive amplifier, with an output exceeding 1000W, a 13A fuse is appropriate).
Cut the European plug off and bare the ends of the wires. Connect the blue and brown wires as shown in this picture:
http://www.bbc.co.uk/h2g2/oldblobs/3403054.gif
(Don't connect anything to the earth terminal).
Check that all the screws are tight and fit the top back on the plug..
Changing a plug is really easy. It's in the National Curriculum for secondary school pupils but many schools teach their 9 and 10 year olds to do it, so it can't be that hard ;-)
Chris