Tourist visa longer than 30 days from Cambodia?

Hi, I'm a Swedish citizen travelling to Cambodia in February and then onwards to China with a possible stop-over in HK to get a visa for the mainland. I was told by a HK visa service agency that it is currently only possible to get a 30-day tourist visa (both single and double-entry avaliable). But I would ideally like to have a longer uninterrupted stay (60 or 90 days). Do you know if it's possible to get this type of visa in Cambodia?