Have you tried contacting the manufacturer of your pop up? That'd be the first place I'd try. If you can sew, it would be much cheaper to make them yourself.
If you can sew, make them out of sheets. This is very easy as you can take advantage of all the hems. Make an open border at the top and slide it onto a thin rod. Cut to the length you want. I have made many curtain with sheets (and there are many designs out there).
You can save yourself a lot of money by purchasing some good used curtains at a Salvation Army Store or Goodwill Store. Take the measurements and you can customize them to fit.
My friend makes custom boat curtains. They're made to withstand moisture & pleated a special way that they easily fold into a small space (like an accordion). She uses the VERY best fabric, but you could also choose your own. She makes them for her brother-in-law that makes custom boats. If you can't find some place else to buy them, this is an option. She charges $400 for the labor & you'd have to buy the fabric (half down & half when you get them). Her price is wholesale. Contact me here on ThriftyFun if you're interested. If it were me, I'd make them myself by modifying another pair of curtains. Also, you could go to a boat or RV show & check out the venders there.
Camping world might have them. If you do not see them on there web site contact them via email and ask them where you can buy them. Also you might want to google the manufactures web site who made your pop up and maybe they sell them or can direct you as to where they can be purchased. If you have no luck ever buying them you could make some. All you need is one of your old ones to use as your pattern or measure the size you need for them. We have an older motor home we bought that had curtains in it I did not like and that had dry rotted so I used them as patterns and make my own from sheets that I had and liked with dragon flies on them and for the bottoms so they did not sway or move out I attached strips of velcro to the bottom curtain backs and to the wall to keep them in place. http://www.campingworld.com/
Login using the form on the top of the page to post feedback (if you are a registered user). If you have not yet registered, click here to do so. It's FREE!.