Marc's right; Google will help, here. Of course, providing samples will depend on what cause you're looking for. It wouldn't do any good to send you Movember pics, only to discover you're raising awareness for ovarian cancer!
Most promotional cause images tend to be non-artistic, and use survivors, simply standing and smiling with an "I'm living through it" look. Bonus points if they're kids or celebrities. It gives it that humanistic look.
Alternately, some go for that fighter/athletic look, kind of that "I can beat this/I did beat this" look. That seems to be the more common of the two, as it not only gives hope to other sufferers, but also tries to convince potential donors that an end is within reach.
Of course, the area affected, or a representative area, also plays a prominent role in the images. Many breast cancer photographs, while the women are covering their breasts, they are topless. For men's health, the November mustache has become the symbol. For cancer in general, it is often a patient (again, woman or child) who has lost their hair to chemotherapy. It all depends on what you're raising awareness of!
I'm planning something similar myself for a cause that's near and dear to me. I'm somewhat lucky, in that what I'm looking to focus on has no outward physical symptoms, so I'll be able to have everyone pose, just like any regular model (yes, they'll all be real sufferers).
Okay, I'll shut up now.