I have a skein of handspun wool and mohair that weighs 10 oz. It wraps at 7 or 8 wraps per inch. I won this yarn in a raffle and have no idea of the yardage. Short of winding a given length warp and then counting the ends I have no idea how to figure how many yards there are. Does anyone have any suggestions?

That is a hard one. I would open up the skein and measure the circumference of it and then count how many strands are in the skein. That should give you a pretty good approximation.

There is something called a mcMorran scale for yarn.
They are not that cheap especially for a one shot deal. If you have a good scale that can weigh a small amount, you could measure and cut a good length that the scale would be able to register. Then weigh the rest of your skein and calculate from there.
Does that make sense?

This is a variation of what Jane mentioned. I use a niddy noddy which is 2 yards around. At the end I count the strands at the beginning and multiply x 2 yards. A McMorran balance will not give the yardage in your bundle, but it will tell you how many yds/# there are in a particular fiber which puts one in the ball park for setts or other weaving calculations by weight.