I personally struggling on buying Bitcoin in Cambodia when I first started to learn and invest in it. That is what has happened to me long times ago.
Since I concerned both physical and financial security then I need to go and buy from our neighbor country creating an bank account and processing some fee for verification (the KYC process at the bank).
Cryptonomad ( Telegram Group )
Cryptonomad more than just a market place but it's is a community who helping each other by sharing the idea on investing, solving some problems. you can join the community here Cryptonomad Telegram Group .
Since it's is a community with real people I do recommend to buy in person.
REMITANO
REMITANO is one of well known P2P exchange and do exist in Cambodia and had served so many crypto investor. I had done few transactions this platform is really secure buy all the transaction has been carefully verify by their staff.
There are fewer local bank that in the list for transaction method.
Another interesting as permention the home page "Instantly earn 89.00 USD for every one of your friends who joins Remitano. Share the link."
Localbitcoins
localbitcoins is the famous Buy and sell bitcoins with Instant, Secure and Private. Their operation has been operand in 16122 cities and 248 countries including United States.
To be secure should be trade face to face.
Facebook Community
Cambodia Cryptocurrency, Bitcoin and Blockchain Community Also a valuable community that share information and helping one another.
Since it is a centralized and privacy concern I don't really encourage you to trade on Facebook.
Bitcoincambodia
Bitcoincambodia Is one of very old and private Bitcoin in Cambodia who has operand their transaction since long time ago. I never done any transaction with this one but according to the people from the community this is trust able but the problem is with price a bit high.
Mekongmonkey
Mekongmonkey this one just like the Bitcoincambodia as well I never done the transaction either.
Conclusion
This is not an investment advise I don't revived any commission from above market as well. So I'm strongly recommend you to carefully research before placing your money. Please let's me know if you hear or have experience with them and others place that we could buy and sell cryptocurrencies in Cambodia because it's will help our community to explore more market.