The Superstore on Eagleson has small bottles of White Truffle Oil for about $10. Nicastro's may have some also, and I believe "Made is France" on Dalhousie has black truffle oil. I actually picked up some great black truffle oil at Homesense a while back.
If you are in the Byward market... The Byward Fruit Market sells truffles and truffle oil, I would call them before you make the trip to see if they have some in stock. I bought some there 6 months ago.
Last time i bought some i got it at Nicastro's in the glebe. ASk at the counter because they have a huge selection of oils so it may be hard to find amongst the clutter
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-M.