We are not in the business yet, but are researching an idea which we truly hope we can produce

We would need tshirts made with custom length sleeves, and possibly a few inches longer than traditional tshirts. Are there any tshirt manufacturers that will provide custom work like this, but without a huge order? These would also be in plus sizes of at least 3X. Organic would be nice, but not required. Btw, I'm in the U.S.
Thanks!