Wow, I am also in the brainstorming process of making a Harley quilt for my BIL. My sister bought and sent me a sheet set she found at Walmart. I did see the sheetset online. The pillowcases have a great logo on both sides (so that's 4 to work with). Plus the sheets have edge fabric with printed flames. In anticipation of making a scrappy quilt, I've been purchasing fabrics in shades of orange and blacks and grays. I have plenty of sketches now but haven't settled on any specific idea.
I made an Ohio State quilt for my brother and there were many OS quilts quilters had sewn for me to look over; but not much out there with the Harley theme (except T-shirt quilts).
Good luck on your endeavor.