So do you know about Spoonflower? This awesome site lets you design and purchase fabric that's printed on demand. If you can't find that perfect fabric, this is the site to go to create it. And in the case of the custom order that I sold today, Spoonflower is also the perfect site if you're hoping for some truly custom buttons.
I had an Etsy shopper contact me earlier this year asking if I would make button accessories from fabric that she would supply since she was going to design it herself. Before she ordered from Spoonflower, she checked with me as to what size her design should be and what the maximum space needed to be between the design as it repeated on the fabric. As you can see, she had fabric printed with the school crest for a school in Georgia and I got to make the buttons into button snap clips and ponytail holders to be sold in the school store. We started with 40 buttons to see how they'll sell, but this one fat quarter has enough crests for another 90 buttons! Getting the text and circles just so was rather difficult, but I think the end result was worth it.