Mark G-J
I'm in the UK and have just replaced the PSU in a D530 SFF with generic 300W one from CPC:
http://cpc.farnell.com/_/mpt-303/psu-300w-atx-tfx1-psu-tfx1-300w/dp/CS11791
It's not an exact replacement, but does fit nicely into the case.
When you first boot up you will get an error message saying "920-Fan Command 2 Pin Connector from Power Supply Not Connected".
The standard HP PSU has a "fan command" connector that isn't present on standard PSUs (a small two pin plug with white/red and black wires).
Simply cut the plug off the old PSU leaving a short length of wire on the plug and connect a 1K resistor between the wires. Plug the connector back into the motherboard and you will no longer get the error message at boot.
Hope this helps.
MG-J