It sounds like the same service which was recently featured in the repeats of the BBC's 'Coast' series on UKTV History.
I've not been able to track it down with a web search but the following information might be of interest:
The Truronian website lists various ways of using their buses to tour the county including, in some cases, some interesting walks. Go here:
http://www.truronian.co.uk/index.cfm?ArticleID =185
Ignore the main content of the page but checkout each one of these links:
Bus Days
Bus Tours
Bus Walks
Bus Map.
If the service you refer to stil exists, it should be listed in the relevant timetable book(s). These can be ordered, for free postal delivery to you, by selecting the guide(s) you require from this page:
http://www.cornwall.gov.uk/index.cfm?articleid =7410
and then either using the link to the online order form or by contacting the Cornwall County Council Passenger Transport Unit. (There's a postal address, e-mail address and phone number on that page. In fact, simply phoning or e-mailing them might be the easiest way to get an answer to your question).
I'm sorry that this post doesn't directly answer your question but I hope that it wil point you in the right direction.
Chris