** I tried to find a replacement locally, but I was told they don't make that particular element anymore. **
If you have a "white" glass cartridge, they are definitely are not being sold any longer as Corning® which made the white glass stove tops for everyone got out of the appliance business 10-15+ years ago. Sorry.
You could install a black glass on it and replacement elements for it (if necessary) or you can purchase a whole replacement cartridge of a different style (see the following link) which should work in place of it.