Import license

You know that may make a difference, usually its personal item shipments that get nailed.  As I understand it your export forwarder at  point of origin generates the paperwork and has to have inspections done to verify what is being shipped then upon arrival you are contacted by the port authority upon arrival. I have only heard from friends second hand.
If you live in SV I think there are at least 2 import companies along the frontage road in front of the port who could help you.  If you are really stuck there are a couple of container storage depots at the top of the hill on the Phnom Penh road just out of town they would able to help.
If you can find a Yellow Pages there will be some in Phnom Penh.  YP's are not easy to find but a bank or a larger hotel may have them.
Sorry I cant help you more, I have heard the horror stories and not wanted to do myself.