I imagine there are some synthetic fragrance oils out there that are cinnamon-scented that wouldn't be dangerous to use in soap. Note that while it probably won't smell exactly like the essential oil, as it isn't actually made from cinnamon, it should smell close enough to be satisfying. Check around on sites that sell fragrance oils for cinnamon scented ones. Saveonscents.com has some for reasonable prices and tips on usage rates, etc. I hope this helps!
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