You can buy them direct from Bunting Magnetics, but I ordered mine from Fritz at NA Graphics because I like to help out small businesses. I’m pretty sure the base ships direct from Bunting. The size I use is 6″ x 9″. It works for almost all my needs.
I started out with metal backed plates and magnetic bases at school, but I’ve switched to using sticky-backed plates on an aluminum base now. I just find them easier to make small adjustments, since they don’t ‘smack’ down onto the base, and I like being able to see through them when putting them in place. I also like the flexibility of the plates, so I can lightly attach them to the printing paper and place them on the base by tripping the carriage.I’m slowing adding to my collection of plates, and they’re also much lighter, and take up less room than metal backed plates as well.
Yes, the adhesive plates are slightly less slightly less expensive than the metal-backed, but buying the adhesive sheets for them might add up to about the same price. I’m not sure about the price difference between the magnetic vs. aluminum bases.