@alisha-- Yea, you're right. A lot of the stuff on the market is synthetic. One way to know whether the ones you find are real or not would be to look at the percentage of methyl salicylate in it. Real wintergreen oil will have around ninety-nine percent methyl slicylate.
The other way to know is to just look at the price. Anything less than $5 per ounce is probably synthetic.
You can also ask about it from your pharmacy. Sometimes they have it too and it's usually the real one (especially if it says "essential oil"). I get mine from my pharmacy.