TM Heera was originally distributed freely by Tamil Murasu and later by various Tamil computing forums. However, (e.g., selling a book set in TM Heera) may require checking the original license. The patched version is typically considered a derivative work, distributed for interoperability.
If you specifically need the TM Heera style, consider from authorized resellers (e.g., Pothi.com or the TM Typeface official channel). Many foundries now offer upgraded Unicode-compliant versions of classic fonts. tm heera tamil font download patched