Like Peter said, if you're looking to save money or are into the DIY stuff, you can build some from hardware you can find at Lowe's or Home Depot. If you go this route, post some follow-up photos as I don't think I've seen anyone do that on the board yet.
For commercially made, I know of only two companies that make magnetic fractionals. PDA and Plate Mates. I've never used Plate Mates but I have used PDA's (both regular fractionals as well as their magnetic ones). The quality is well worth the cost, imo. Not to mention the customer service second to none. I've bought a lot of equipment and no other company comes close to the customer service you get from PDA. Pricey? Yea, but they'll last forever. You can check them out at http://www.fractionalplates.com
Hope that helps and let us know what you do.