I think I ordered a custom one from Backdrop outlet where they sewed two 10x15 together but I am not 100%. I would give them a call and ask them. I have bought a lot from them so that is why I think that is the company that can do that. I will say the challenge becomes hanging something that big. I have custom built a backdrop stand that holds a 30x15 but it is a lot of work setting it up
But check with a sail maker or awning maker. When they tack "photo" onto stuff, it jacks the price fourfold. You might find what you need more cheaply from a sail maker or an awning supply on the web. Heck, what you need may be an off-the-shelf item for sailing vessels.
I made by own. I dyed it with Rit Dye a medium gray color, left the dye in the machine; took the muslin out and hung it on a clothes line (yes, we had one!) and used a spray bottle with a bleach solution, sprayed a streaking dot pattern all over it.
Put it back in the machine to agitate a bit longer in the dye, sprayed it again.
Till I more or less liked the results.
Washed it as instructed, then didn't really like the results. Being on a very tight budget at the time, I used it for a few sessions after I was through with the regular stuff — just to test the results.
It became my most popular background. When I sold the studio equipment some years later, it went real quick, and for a nice profit!
