I think that you are wanting to know which spokes to detension first so that you don't further damage the rim. This is only a guess but I would loosen the drive side spokes opposite the broken spokes first by one turn and then loosen the other drive side spokes by one half turn and repeat the process until all the spokes on the drive side were lose. I would not loosen the non drive side spokes because as the drive side spokes are loosened the tension will be removed from the non drive side spokes as the hub moves toward the non drive side.

I have been able to buy single spokes at a bike shop. If you only want to replace the broken spokes, then take a good spoke from the drive side to your bike shop and see if they have any of the correct length and size. The last time that I bought spokes they were around $1 each. They probably cost more now.