I think what you're looking for isn't a verb conjugation, it's the word はず or
hazu. As an example of how it works, first start off with the basic sentence:-
さがデジカメを探している。
dejikame wo sagashite iru.
I am looking for the digital cameras.
..and then add はずだ (hazu da) or はずです (hazu desu) depending on politeness level:-
さがデジカメを探している
はずだ。
dejikame wo sagashite iru hazu da. I am
supposed to be looking for the digital cameras.
You can find more on Tae Kim's
The Way Things Should Be page and Maggie Sensie's
How and When to use Hazu page.
マイケル