sounds like a cool project!!!!. check out ebay. the Petty ones are always on there. there must of been the Petty ones and Taiwainese copies as i have a white on that doesnt have the PP logo. be prepared to pay about $300 AU if you want a NOS yellow one though. im sure some guys on this forum will have one for you though. see if you can get one with the black brackets that clamp to the forks. this was an updated design from the late 70's instead of just zip tying the light to the forks
ahh just remembered when i was typing this, you can buy new Petty lights here! -http://www.strictlyhodaka.com/prestonpetty.html better than stuffing aroound and sanding back an old one