They'll have it. Take your Buddha down to the hardware store, go to the stainless steel screws, and try them until you find the right size. I don't know the size, or if it's metric or standard, but they'll be happy to let you find a replacement, and may even help you find one.
You'll also need an O-ring, though. They might or might not have that. If not, you'll know the right screw size after you've found one at the hardware store, so you can order an O-ring that size online.