My mind immediately turned to "search" thoughts. I put this into my browser's search box:
fabric AND "Route 66" AND "Harley Davison" OR motorcycle
You say you aren't "a tech. person" so copy and paste that search or write it down long-hand exactly like you see it above. I came up with some links to buy FABRIC consistent with a motorcycle/Harley theme. Route 66 is a VERY famous highway that your roadie friend would certainly know about.
To keep your motorcycle themed quilt from being too bright and flashy talk to an expert at your local quilt shop about how to incorporate some themed fabric (which I am assuming might be bright and flashy) in with some more sedate and vintage fabrics to end up with the effect you want while still honoring your theme.
If you know someone who has an embroidery sewing machine, maybe you could get them to embroider a motorcycle (in your friend's favorite color ... or a color from your theme fabric) onto fabric pieces that you could feature at the corners of a center medallion or at the outside corners of the quilt. You also might look at motorcycle tires and think about how you could adapt the tread pattern to make a quilting pattern for a border quilting treatment. If your friend belongs to a motorcycle club, you might look at the club's logo to see if you can pull something out of it to incorporate into your project to make it that much more special to your friend. And his club's "colors" might also suggest which direction you want your more sedate fabric choices to lean, but if you know his wife prefers a different colorway in the family den where you expect your quilt to find a home stick with the other colorway. LOL