I couldn't find any measurements online either. If you can't get reliable results pulling your own TSPs or don't feel comfortable doing it or whatever, here's what I would do: build a 0.5 ft^3 enclosure per side (2 drivers per enclosure). Use a 2" diameter vent that's ~3" long per enclosure. That should give you a tuning of about 55-60hz. That's a good generic place to start. You might get better results by trimming them down a bit to raise tuning depending on where the fs of the speakers are and how high you plan to cross them over to the subwoofer. It might take a bit of experimenting but 2" PVC is really inexpensive.
If they don't sound right and/or you're not planning to use a high pass crossover on them, pull the port and plug the hole giving you a 0.5 ft^3 sealed enclosure. This may or may not give you a generous midbass bump, but should allow you to at least run full range if you wanted without worrying about unloading too much at bass frequencies.