I am so very sorry for your loss.
The best thing to do will be to get him some new companions as quickly as possible. You may not be able to put them together right away, but you can put them where he can hear them and they can "talk" to each other. Do whatever you can to distract him.
I agree about the Rescue Remedy. Rooster Booster is another good product you might try.
I agree about the Rescue Remedy. Rooster Booster is another good product you might try.