I used to sell woodstoves and patio/bbq furnishings. A pretty good mixture of seasonal markets.
The patio furniture came in during January. It was sale priced until Easter /March and the local Home Show when full retail was charged for about a week.
That was also when we sold the most both in numbers and in values.
Then we had our Spring Sale, followed by Mother's Day Sale, Followed by the Father's Day Sale, after which no one bought any patio furniture or bbq equipment.
We were a specialty store and the stuff was still in the storage bay.
By mid-July we were booking woodstove installations which were strong until mid-November when they dropped dead and we had effectively no Christmas related business.
Seriously though. We just had no customers interested in buying during the 'appropriate' season.
For your question though, I would avoid the chain stores, whose out of season stock is warehoused away from the retail store. Instead go to small local sellers.
Or the Sears catalogue. The catalogue is usually good for eight months, even after the next catalogue has come out. And they will give you the sale price even if you order from the main book.
Oh and if you are buying patio furniture this year, you will get the lowest prices and the widest choice in January and February.