Here are two on-line resources:
- The USPS International Mail Manual. For this to work right, you need to have Adobe Acrobat set up as a plug-in for your browser. Click on the "International Country Listings" link, and click on the page number for Cambodia. There is a lot of information there.
- The Universal Postal Union has information on address standards for most countries. Click on the "Postal addresses" link on the left and then the "Postal addressing systems" link. Select your country, and you'll get information about how addresses are formatted and a sample address. There's not much there for Cambodia, but this is a good resource to have.
Your best bet, particularly with a package, would be to go down to your local Post Office and talk to them directly. Good luck.