Try T. Rutlands or Dennis McCann Ferrari parts. T Rutlands is usually cheaper, but I don't know about availability of V12 blocks. McCann will be more expensive, but more likely to have what you need. FWIW
Old post thou ... But don't know if you are still interestedI am looking to buy a 12 cylinder block with pistons. I don't need anything else. Block doesn't even need to be repairable. Please let me know if you have something or if you know of a place I can look.