Diametric ring magnets available at mjbots.com
To go with the new MA600 breakout board, mjbots.com is now stocking diametrically magnetized ring magnets:
For now, the only size is 32mm x 22mm x 4mm, but there may be more in the future. These are magnetized through the radius, not axially, so they are suited for use with off axis magnetic encoders. Check it out!