sit for a second, turn your speakers up, listen and watch closely when you click the play button here:
YouTube - HexiBase's Channel
this will help dispell the myth you are limiting yourself with by choosing a tuning frequency as your goal or handicap/contingency to reaching that goal. what professional dictated that your goal necessitates the use of a bass reflex or "ported" box? If your goal required the use of a tapered transmission line or a rear loading horn to make the sub do what you want, would not having a "tuning frequency of X" cause the whole project to be scrapped? If not and the goal is still the same, no matter what it takes to make it happen....then i implore you to read up on the pwkdesigns.com website a little and fill in the request form. going that far is relatively simple and free. i'd recommend you watch as many of the box related videos on his youtube channel as you can to learn a little more about what's going on.
good luck.