Look for motorcycle big bike

Perhaps I could offer a suggestion or few.

Check out the need for licences as some countries require different licences for larger bikes.
Check out the state of the roads to see if a bike of the type you're interested in is any use over there.
Check out insurances for large bikes.

It's possible to have bigger bikes here but you're going to have to jump through a few hoops and red tape. 250cc is generally the biggest bike you see around and that used to be the max engine size allowed by law. I think this law has been changed, or is in the works to be changed.

Truthfully, a 250cc bike is plenty in Laos. The roads aren't fantastic and with technology today, 250cc bikes have plenty of power for cruising.

Finding something bigger will be touch and go and when you do it will be expensive. I know a shop that has 2 Harley Davidson 883 Sporsters for sale, both used but in excellent shape, and they want more than a brand new one would cost in the West. About US$12K I think.