I have ordered magnets from United Nuclear. They are supposedly the most powerful variety available, and I'm pretty sure they are the ones used in the original implant experiments. They are my starting point.
Several companies specialize in Parylene coating and I have contacted a few. I was very pleased when a company wrote back saying they could indeed coat the magnets. As of right now I am working out the details and trying to do it with a limited budget. If I were to ship them magnets to coat, they would charge $500 for a batch. This is a standard "engineering run" price for them. The quote was for 20 magnets at this price, but it's possible to get more in.
If this is the only option, I have no problem investing this money. I thought about selling the remainder of the implant-ready magnets to recover the cost if it does indeed work, but it would be wholly irresponsible on my part to do so. At no point do I want to be known as "that guy selling faulty implants." Instead, I will probably ship them to prominent body artists for examination or further testing.
The company that responded to me also manufactures and magnetizes coated magnets in-house, which may be better and less expensive than shipping them magnets which I purchase. More on this after I get responses from them.
Apparently, coating an already magnetized magnet is more difficult than a non-magnetized one. I can only assume that the coating machine has ferrous components that the magnet would attract and stick to. It can be done, but an unmagnetized part is reportedly much easier to coat.
A local company stated that the magnets would be too difficult to coat while magnetized, but I plan to visit them in person once my magnets come in the mail. An in-person chat with somebody who knows their stuff will be very beneficial.