Hi Carole,
There is definitely some difficulty finding open resources in some subject areas. In my experience, much of the focus so far has been on STEM subjects and those which have high enrolments. The project I'm working on falls into the latter category. That said, I am definitely seeing movement in the direction of sharing resources in other areas as awareness of OER becomes greater. I think many instructors are feeling as you do, that they would like to use OER, but have a tough time finding them. We have a list of places to look on our website which may be helpful to you.
In week 4 of this workshop, Clint Lalonde will be looking at finding, evaluating and modifying existing OER, so you'll get some guidance there.