Well, I know in the 70's models of Puchs, it was true. I don't know if they changed that or not...
You can, however, use replacement 12v bulbs even in a 6v system, I've been told, but they'll run really dim. My advice, look for an old car parts store (like a vintage, 20's-ish place?) for light bulbs. I'm lucky enough to have one of these right down the street from me so I can get head/tail lights all the time... hahaha.
Also, for parts check out ikesbikes.com (call or e-mail works best, his site is kind of bare), themopedjunkyard.com (the site's a little sketchy looking but I've done some considerable business with them, good guys.), mopedwarehouse.com (he does have more than he's got listed, but sometimes takes a while to answer e-mails... gets really backed up and all.), or handybikes on e-bay usually has good stuff. Also, I've never gone through them, but apparently 1977mopeds.com are really cool guys?
Welcome to the site, have fun!