My hotel provides bicycles, but the seats are much too short, even with the post fully extended.
As a side note, I've never found a city bike in Asia that's tall enough to fit a 185 cm rider like me.
I rode Mobikes and Ofo bikes in China, by the dozen. Never could get the seat high enough on any of them.
Here in Siem Reap, some bike rental places have good mountain bikes that a tall man can use.
Right now I'm staying in a hotel that has some bikes, but they're "city" bikes and too short.
I need to find a bicycle shop with a parts inventory that includes seat posts.
Tall order?
Anyway, where do y'all get bicycle parts?

I have always found long seat posts quickly and easily. Just go to bicycle shops and ask.

If you cant speak Khmer, it should not be too difficult to communicate in sign language. Some shops have people who speak English.

Be aware, seat posts come in different diameters, you need to get the correct one for the bike.

If you are using it on different hire bikes, I would get a seat too, so it is easy to swap.

If you are staying for some time, you could buy your own bicycle. You could buy a new mountain bike for a little over $100. I would only get one with disc brakes.

You can easily travel with a bicycle on the back of a minivan.

edit= dopey me somehow I read Sihanoukville instesd of S R