I called this morning to the official (free) site per Rick's book and the message said they were taking reservations for as early as September 29. However, we didn't need them until the 6th of October. I was put on hold for 5 minutes waiting for someone on the English option and gave up. My brother who speaks some Italian got through much quicker and made reservations so if you know someone who speaks Italian, it could be a lot cheaper to call from the states.
Just to let you know...we arrived in Florence a few weeks ago and didn't have res. for the Uffitzi...so we just walked over to see what would work out. The line to get in (people without res.) was pretty long. So we went into the reservations office and made res. for later in the day! We returned 3 hours later and walked right in! The same for the Academia museum. We had a 15 min. wait out in the line and then got right in! So even if you don't have reservations, sometimes you can just walk over and get lucky!
Tom and Sherry Trojanowski