Im sure if you send bubbleman a message he would accomodate you somehow. I dont know if they sell singles but if you want to go with original bubblebags he may send you one.
It was 6-8 yrs ago I had one bag rip and he sent me a replacement. I cant remember if he charged me or not, I think I paid for shipping... if he did it was minimal. I did get the bags from him in the first place however. BM is a cool guy shoot him a pm or contact via his site.
Much easier and cheaper these days to walk into your local hydro shop. If they dont stock they may be able to order it for you...