This may be a bit late but I hope it helps someone in the future. It looks like RS sell suitable 230v to 24VAC 800mA PSU for around £11 delivered. http://uk.rs-online.com/web/p/products/7300247/ .They also sell one with a European plug. CPC Farnell also sell a 24VAC 750mA psu, however that one has no inbuilt plug http://cpc.farnell.com/stontronics/t3445sa/inline-ac-ac-psu-24v-0-75a-bare/dp/PW02881?ost=power+supply&categoryId=700000010071
Just for completeness this has already been posted on here before
I cannot see any reference the AC or DC I assume however it’s AC as it says it suitable for most 24V sprinkler systems.
details of Orbit’s transformer.
I am sure there are other PSUs available but all of these seem reasonably priced.