Any suggestions for a tour guide in Invergordon for one day?
I see no one has answered so I'll give it a go. Are you traveling to Invergordon as a day trip from somewhere else, such as Inverness or Edinburgh? Or will you be staying in Invergordon? Or arriving there on a cruise ship? (I see it is a popular port for cruise lines.)
You have probably already read this site, with the various excursions listed that are, alas, not in Invergordon itself.
But, the Naval Museum & Heritage Centre and a mural walk in town are mentioned. It looks like you can do the latter as a self-guided walk. The local tourism authority has hosts that meet incoming ships http://www.visitinvergordon.com/hosts.html
They state that there are independent tour companies you can contact directly http://www.visitinvergordon.com/tours.html although some of these, again, seem to focus on tours outside of the town.
You could also email the tourism office and ask for recommendations for a guide to suit your interests. Be aware they probably work part time, especially in the off season, so it may take a few days to get an answer: firstname.lastname@example.org