Would RV manufacturer have extra accessories for purchase?

You need to contact an RV dealer who sells that particular brand of TT, but some of the larger RV parts houses may be able to help you out too. Another solution which may end up costing less and be better quality is to have a seamstress make a curtain for you, good place to find out who does sewing is go to a fabric store like JoAnn's or something. Camping World probably has the little hooks or whatever you need to clip onto the new curtain.