This past season, double-breasted suits, especially in that price range (as stated by the OP -$500-$1000) have been rather scarce - Brooks didn't do any D/B or three-piece suits this past season, and I don't remember seeing many around.
Best of luck looking, but don't be surprised if you're disappointed in the available selection RTW.
Look for a Polo on E-Bay. There are plenty to be had NWT in the lower end of that spectrum.
Polo makes great DB suits. Paul Stuart does too. If you're not in a rush, keep checking eBay until one in your size comes up. I even got a great DB suit from Domenico Spano on eBay for very little. I saw a DB on display in Brooks Brothers a few days ago, but the cut just looked off. At least they no longer try to put single vents on double-breasted suits. In their mind it made them more conservative. In reality it just was a mistake.
To be honest, I would not think of many occasions to wear a DB suit, I just really like the look of it if impeccably tailored. Plus, I live in Canada, so even less occasions to wear DB. Guess this means I have plenty of time to wait for my size to come up. (40L )