Miller, I don't think he means whether or not the bead itself will be attracted to a magnet, but rather does someone makes a magnetic attachment, that holds itself on the rib, that has an ivory bead.
JMB501, am I reading your post right? If so, no one that I am aware of sells one. Don't know if it would be possible to remove the light gathering "bead" from one and replace it with an ivory bead or not. I guess you could try.
I don't think it would look right, even if you could. Ivory beads and magnetic add on bases just don't seem to go together, to me. But it's your dime, and you may feel differently.
Good luck, SRH