Seeed is currently out of stock of the Bus Pirate v3. The next batch should start shipping in a week or two. In the mean time, you can should soon be able to place a back order with Seeed, or pick up a Bus Pirate (and probe cable) at Adafruit.
The next batch of Bus Pirates from Seeed may will be the v3b revision. This is still up in the air, we sent the files but don’t have confirmation they were actually used. V3b is exactly the same size and has the same capabilities as the v3a, we just made a few tweaks to improve manufacturing reliability. We’ll cover the update in an upcoming article, or you can read a bit about the major updates in the forum.