reftex-use-external-file-finders

reftex-use-external-file-finders is a variable defined in `reftex-vars.el'.
Its value is

nil

Documentation:
Non-nil means, use external programs to find files.
Normally, RefTeX searches the paths given in the environment variables
TEXINPUTS and BIBINPUTS to find TeX files and BibTeX database files.
With this option turned on, it calls an external program specified in the
option `reftex-external-file-finders' instead. As a side effect,
the variables `reftex-texpath-environment-variables' and
`reftex-bibpath-environment-variables' will be ignored.

You can customize this variable.