Mike,
I have never reported on range extensions in a scientific note like those that occur in Herp. Review. So have no experience in that regard. There is a grad student (name escapes me now) under professor Darda at Central or is it Eastern Wash. St. U. in Ellensburg that has done that sort of thing so you might contact those folks.
As far as a new species is concerned, that is another ball of wax and I suspect that each journal has its own standards to follow. I am in that very process with describing the new species of Sharp-tailed Snake (Contia) that occurs in Calif. and Oregon. What I have done in preparing a draft is copy the format that occurs in Herpetologica for formally describing a new species.
To convince the editors / reviewers you will need solid data usually with statistical treatment. The paper I published that described the discovery of the new species of Contia (not the same as a formal description of the species mentioned above) was rejected by 5 of 6 PhD reviewers, two of them associate editors. The editor remained neutral and luckily, one reviewer knew his stuff and recognized the significance of the data I presented. So it can be a long and frustrating experience if one does not have credentials which is the situation both of us are in. It actually took me one year to gather the supporting data that made the discovery a slam dunk but an additional two years to have the various drafts reviewed and rejected, I was finally able to convince the editor of the validity of my data thanks to that one reviewer.
My advice is to seek out a professional that would be willing to cooperate on such a project.
Richard F. Hoyer