While FileMaker Pro 12 (and its Advanced counterpart) was a landmark release that introduced the .fmp12 file format still used today, it is now considered "legacy" software.
Secondary Markets: You may find genuine, unused license key cards or full retail versions on sites like eBay. Filemaker Pro Advanced 12 License Key
Additional Resources
Custom Menus & Functions: Create tailored menus for different platforms (including iOS) and build reusable custom functions. While FileMaker Pro 12 (and its Advanced counterpart)