If you cannot find a "Z Full" package, a standard file for the CK13i will work just as well. The "Z Full" is mostly a labeling relic from early firmware packers. Look for any file ending in .ftf with a matching CDA (Customization ID) for your region.
: You need three primary files to complete a "full" flash: MAIN : The core operating system file. FS (File System) : Contains regional settings and languages. sony ericsson ck13i flash file z full