You can get it from most any RV supply store, or online.
Mine did the same... and last summer, it kept coming out of the track over the generator door where it curves up towards the nose, and began flapping while I was going down the road. I'd pull over, tuck it back in, and that'd work for a day or so. Next trip, same thing.
About the 4th or 5th time I'd had enough. Got my screw gun and a couple of self-tapping screws, and put 1 on each side through the trim right at the apex of the curve. Yeah, I can see the screw heads if I look for them, but I've had no trouble since.