Your post made me curious. I knew that Yunzi stones are a little bigger (in width) compared to standard / Japanese stones and do not fit a japanese board very well but it appears that there are different sizes!
(From Yellow Mountain website)
(From wikipedia website)
Your set is definitely not going to fit any standard size board. Finding a suitable one might prove quite a challenge. The fastest and cheapest option is make one yourself. There is a thread on that topic which can help you out.
Good luck!