I got my wishbones from Saturn/NTS.
Last I heard Gillham had taken ownership of the Saturn MX5 design and was planning to supply parts and develop it further, so it's probably worth talking to him if you want to go the Saturn route.
I did suffer from the dreaded diff arm breakage... but that was due to my terrible idea on how to mount it
I've covered about 1000 miles since I replaced the diff and changed from rubber to hard mounting, so it's looking promising!