Not sure but you might be able to get them through a place called Asti Magnetics. I don't have their new phone number since they were bought out by EVG. I used to be on their mailing list and I recall seeing a list/cross for C pickups. Thee "magnetics" part is from when they specialized in after market transformers for TVs. Then they went into video heads for a while.

I have no idea of their sources but their products were usually good. The problematic ones were not just problematic for them. Certain things are just troublesome it seems.