Here are a few suggestions, to get you started:

Before you go and buy something, check out your closet, there might be some forgotten
​pieces that you can give a second life to.​ If there's nothing to work with there, then:
Visit your local craft store for 100% recyclable polyester felt. 
Cork leather: The Little British Fabric Shop
Wool felt: Filzfelt
Miscellaneous sustainable fabrics: Pure Fabricz​ &  Offset Warehouse
For a wider list of online shops that sell sustainable materials you can check out Refinity