Hi Julian,
Just been having a look round online for you.
Ive found
this one. 240v AC>24VDC 2.2A, seems a bit expensive though, £22.95 (plus P&P at a guess) and it looks like its used.
I also found
this one on ebay 240V AC>24V DV, 2.5A, £16.99 + £4 P&P. Still expensive but at least its new
Found
this one on ebay too. 240V>24V DC max 5A £4 + £12 P&P
Hopefully you will be able to get one off someone on the boards cheaper but thats a couple of possible options if not.