The texi2mdoc utility is a converter from Texinfo into mdoc.
It is a standalone ISC-licensed ISO C utility
and should compile on any modern UNIX system.
For the time being, contact the mandoc mailing list with
questions, but please make sure any formatting issue hasn't already been covered in the manual.
texi2mdoc is available over anoncvs,
with the module being texi2mdoc instead of mandoc as noted in the instructions.
You can also browse via CVSweb.