I agree with Dawn regarding a rabbit vet, or even a dog vet should be able to amputate a let, provided they have proper, safe anesthesia. Find a vet in your town and call them.
Your chin should not be limping around. Put him in a small pet carrier where he will have minimal movement so the leg does not continue to cause him so much pain, then get him to a vet immediately. After the leg is amputated, you will need that small pet carrier for a while anyway to restrict his movement until the stump fully heals.