If your not in a hurry, watch on ebay. I've seen silver pieces from halters and headstalls sold in lots or individually.
I think there used to be some FB pages for buying and selling Dale Chavez stuff. You might luck out on a silver plate with the same pattern.
A silver maker we used buy silver from when hubby was making custom headstalls sold halter plates but I just checked and they didn't have any at all.
You can try Montana Silversmiths but note their silver is electroplate and looks different against sterling which Dale Chazev is. Even against the bright cut which Montana Silversmiths tries to emulate.
Getting a silversmith to replicate it is an option but usually silversmiths prefer not to do so. Budding new silversmiths might give it a try.
If you're dead set on all matching silver you could sell the silver that's on it and put the money new set to put on or a new halter.
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.
PLAYBOYS OKIE CODY "HOOEY" 10/21/2019