Have you contacted your vet? Vets often know of people looking for animals - thats how my friend got her JR and another got a cat. Would happily have him/her if I didn't already have a pack (2xLabs, a Springer and a JR)!!!
What about fitting a basket muzzle on the dog when he is around the cats. Obviously the dog should not be unsupervised totally when wearing the muzzle in case it is sick etc but at least you can let the dog out of your sight and know it can't hurt the cats. If the muzzle is persisted with you may find the dog loses some of the inclination as it can't bite/kill!
i have a large black cat you can borrow to scare the JR from chasing cats! he has beaten my staffie into submission every time! lol ! good luck in finding him a new home.