first i typed
calendar poster
then
calendar AND poster
then
calendar AND poster AND year ... this turned up "Full Year '07 Poster Calendar..." in the page title of the first result
then i ended up with
"poster calendar" OR "calendar poster" and i would have just checked as many results as possible for a long time....
but then not everyone has my seo skills
upon getting no good results i would have also tried:
12 month calendar page
year calendar page
full "calendar on single page"
full calendar "on single page"
...etc
i think your best bet is just to optimise for calendars generally, and maybe also posters.
try this tool:
https://adwords.google.com/select/KeywordToolExternal
good luck!