I tried to help someone with a similar need a year or two ago and the conclusion was that spares are not easily sourced in the UK. The only site I've ever found with spares was a USA one...
-Kite Pumps (Elec/Man) : WindBone KiteBoarding, KiteBuddy KiteSurfing
By the time customs and postage was added from the USA it was cheaper to buy a complete new pump over here.
I rate my digital HP Bravo highly when it suits to use but I accept their reliability isn't the best despite mine being OK over 3+yrs so far.