This was a reply I received a few years ago when our passenger side window was damaged during an attempted break-in. The WRV part won't help much now
this reply came from this e-mail address to the Alpine window manufacturer...CSHehrLA@hehrintl.com
Duncan (glass replacement) also helped in getting the proper window.
Please contact our Distributor Interstate Metal Fabricators at 800-587-3463. You may also order this through Western RV's parts department. You will first need the part # of the window which you can obtain from Western RV. For an insulated window, we recommend replacing the entire window because you'll probably spend more money in labor to a repair shop to replace this for you. It's easier and faster to remove & reinstall the window. But, it's your choice if you still want to order the sliding portion only.
Hope this helps