It appears that a floating jazz pickup, is nothing more than a mini-humbucker, that includes a cover with a mounting bracket attached?
So probably any mini hum kit would work, as long as you have the proper cover.
You can buy the covers from AllParts, though they are quite pricy.
So another alternative I would persue, is making a neck bracket, and attaching it to a regular mini cover.
You could simply solder the bracket to the cover.
Or you could use small rivets, or both rivets and solder.
Please let us know what all you come up with.