You probably know that there are a lot more activities for the Sunfish compared to the Zuma. But if you prefer sailing all by yourself, or with just another person/crew, a Zuma might fit you just fine.
In addition, to the usual sources (this forum, E-bay, Craig's list, newspaper ads, and 'for sale' signs at your local sailing club), you can look at the Vanguard site for boats for sale.
And don't forget yard sales around lakes and just asking around. Often someone (or their parents or grandparents) will have a Sunfish in a garage or barn that they haven't used in eons and it's just waiting for the right person to ask at the right time.
Welcome! If you decide on Sunfish I'll give the first encouragement for joining the Class association available through www.sunfishclass.org and click on "join the Class."