As far as used supplies go, you might try looking for a Heathkit IP-17 or an HP 711A. Both are only good for 100mA continuous output so they don't quite match your specs, but they do show up occasionally on eBay. The Heath goes to 400V; the HP to 500. I don't know how common they'd be in Europe, nor how much shipping might be from the US, but there are two possibilities at least.
-Pat