Are you speaking of the plexiglass windows
that are held in with black rubber/lockstrip molding?
I don't know about easy/fast in your specific area, but you can order them from Scamp
IF your windows
are the same size. Or, you can take your old windows to a plastics place and have them cut locally. You then have your choice of type of plastic, tint, etc. I imagine that would be the quickest and most accurate.
If you are replacing them, I would use new molding as well. You can also buy that from Scamp
(again, if same size), or, the stuff and tools are made by C R Laurence, and you can find out from them if they will sell it to you or where you can order it. This way you can be sure to get the size that accounts for your plastic window thickness and your trailer shell thickness (in case it is not the same as Scamp).
CRL Auto Glass Weatherstrips and Moldings