I believe the Byward Fruit Market has truffles in jars throughout the year. You can find them at the front beside the cash. But, they also get fresh black winter truffles starting sometime in December.
You likely will not see them out on display but if you speak with the owner (Isaac) he can tell you what they have available and what they are expecting in their upcoming shipment. The truffles in a jar will suit you if you need to get them out of season but they are nothing like the fresh ones.
The quality of all the produce is always good and there are careful to sell good quality truffles as well. The ones I bought in the Christmas of 2007 were incredible.
Chimichimi