Protocol emailing R Package creators
Assuming that the documentation does not explicitly tell you not to email the maintainers about bugs, and assuming that there's not a forum, bug-tracker, etc. for the package, then I think it would be perfectly reasonable to contact one of them via the email address they provide in the documentation.

If they provide no other means of reporting bugs in the package, then I don't think they'd have any justification for taking offence at being contacted at an address they provide alongside the package.