if you don't know what commit is good, just go way way way back. Go back 10,000 commits instead of 1,000. The magic of bisection search is that opening your search window by 10x only adds 3 (well, 3.332) extra bisections.
The actual way to do it is to go back in exponentially larger steps until you reach a good commit. 1, 2, 4, 8, ... Then you already know that the bad commit is between 2^{k-1}st and 2^{k}th commit.