That grinder was made by Kingston-Conley, who also made similar grinders for other companies in the 40's/50's (ie, Atlas, Miller Falls, Walker-Turner). While spare parts are rare, at least you know there will be alternative brands to search from. That's a really nice grinder, and the "slow" version that runs at 1750 rpm. Essentially intended for tool sharpening, not production grinding.
To convert back to 220volt operation you would need to separate the winding sections and wire them in series. For 110volt use they would be wired in parallel, assuming they used a conventional winding configuration. With no colors codes it will be tricky to find the winding halves, as well as the starting windings. If it runs on 110 now, I would leave it alone.
BTW, it is possible that it is still wired for 220, but that the previous owned just slapped on a 120v plug. It will run but have only 1/4 the normal power.