I know of a good rebuilder in Cave Creek, Arizona (near Phoenix). They specialize in old Steinways and Mason & Hamlins. They do soundboard replacements if absolutely necessary. I wouldn't recoment a new board unless the old one is absolutely shot. They can also repair the original boards with shims... etc... They do everything. Their prices are reasonable also. They did a rebulid job for my teacher a while back, he is very happy with it. If you give me your e-mail address I will send you the shop's contact info. There are also has a couple O's at the shop that he will sell rebuilt. One is NY and the other is Hamburg.
Nic