I checked out also to do a PCR-test at Schiphol Amsterdam-airport, until i found out what the price was.
You get results in 6 houres, but 220 euros: https://spoedteststraat.nl/.
As usual in the airport you get teh "easiest" solution, but also the most expensive-one (anybody knows more expensive ??). Because i had to fly on a monday, it was a little hard to find a place where they would do it on a saturday and get the results in time. The official price (in Belgium) was set up as max 55 euros, but strangely after 2.5 months, i still didnt get a bill from it. And also, when landing here (in Phuket), i had some trouble because on the paperwork wasnt written the word "PCR" before the test. But after some discussion, they let me through !! And if coming to Cambodia, the rubber-stamp-issue would cause also a problem, in Belgium, the results are always send you online through a kind of "health-platform" which is only accesable with you id-card and of course no rubber stamp overthere. I think here in phuket they do love rubber-stamps as much as in PP and wouldnt be an issue if flying out from here !!

When we flew back last year it was still difficult to get a PCR test in the area of the US and the international travel requirements airlines were using still said 72 hours prior to arrival. I arranged to get a test late afternoon and get the results printed out the same day. We flew from East Coast of the US the next morning with a very tight connection in Detroit to Seoul. The timing of the test left us the possibility of still being allowed into Cambodia if there was an issue with the flight from Seoul to PP as I believe there was only one flight a day at that time (so I could hypothetically land one day later at 1 am and just be under the 72 hour rule as my test was at 3pm 70 hours prior). Of course, trying to explain that to an immigration officer at 1am wouldn't be something I'd like to try.

So it is possible to meet the requirement from the East Coast of the US, but it certainly leaves little margin for error should things go wrong.