Cinnamon has been a surprisingly widely touted addition to a diabetes fighting diet.
There are a number of OTC supplements that are claimed to "cure" or "reverse" or otherwise have some beneficial effects. Any particular one may or may not help. This is where frequent testing comes in. If you take one of the supplements, and can't see any effects on your readings, you may want to question if it really is doing anything, especially as some of the supplements can get pricey.
I tried some the first year or so I was diagnosed and found, at best, a less than 10 point reduction in my sugars. Helpful, but a long way from a cure. Eventually, they stopped having any effect.
None are a substitute for all of the things you already know you have to do.