I believe that your tiller was made by Gilson, so you might try searching for Gilson and/or Montgomery Wards tiller (Gilson also made MW). Gilson is now owned by Lawn Boy (who is owned by somebody else), so if you have a Lawn Boy dealer in your area he might be able to help.

A search of this forum turned up a belt question about Spiegel tillers, and you can find the response at the link below.

Good luck.

Here is a link that might be useful: Old Spiegel tiller