Just leave your peas on the vine until they are dry and crispy - just as you would for drying beans. If you want the space for something else though, pull the vines or just the pods and put them in an open cardboard box, or a mesh bag so that they continue to dry on their own before you shell them. Air circulation is the key when you do that.
I don’t think the black spot will effect the pea seed. That disease needs moist plant tissue to grow on, not the seeds themselves.
I could use the space, and if pulling the whole plant and letting it continue to dried that way will result in mature seeds, I’ll do that.