Well new is your most likely option unless you want to troll ebay.
cyclexchange.net has them also for the 73-78 but they might be able to do a 72, but you would want to call and ask.
You can also try
http://www.frankmain.qpg.com/Another option would be to just swap the forks and legs both to a 73 or later.
The ride IS the adventure. The destination is just to get gas!