Thomson Financial compiles hard financial data on spin-offs and split-offs. You can get Thomson Financial data through Thomson ONE (formerly SDC Platinum) if you subscribe, or by calling Thomson Financial (888-989-8373), although calling in requests is expensive.
Alternatively, selected data is available in the TFSD Worldwide Mergers & Acquisitions database, available on Lexis (COMPNY;SDCMA), Westlaw (SDC-M&A), Lexis (COMPNY;SDCMA) and Dialog (File 551).