I found the reliability of 1993 or higher very comforting but I never really loved the the Spider versions lines. GTS's and GTB's were very hard to find. This mean't the SS was the only car for me. I looked at 4 but fell in love with one in Texas. Shipping was more expensive than I thought.
Enough about my baby, lets get one for you. I found the www.Autotrader.com
site very helpful although I did not find my SS there. You can set up searches for any model, distance, multiple cars, and other nice features. The site can also be set up through a login to notify you by email when a new 348 (or whatever you are searching for) comes on the market.
I did find a few 348's through other sources like www.ferrariclubofamerica.org
but quickley discovered that the slower posting times of that site mean't the cars were sold before I could call. Another site that seems to have a lot to look at is www.luxcarnet.com
I caution you about them. They are a remote broker that does not ever see the car they are selling. When you call them, they get basic info for you but need to establish a brokerage deal with the seller before you get specifics. I wasn't crazy about that style.
A site you should be aware of if you end up with a 348 is http://www.club348.com/
AL kinds of very useful info in the technical section.
Let me know if theres anything else I can help with