I can't remember if I ever sent the email I was composing in my head to UltraPro and BCW about getting off their asses and making a booklet card holder. I realized that booklet cards were at the time fairly rare and new to the hobby a few years ago. But now you find them in almost every product from entry level to super high end. Well UltraPro finally has come through. Available in two thickness (185 and 187mm) these guys will run you about 10 bucks a piece right now. At least the ones I've found online. I have yet to see these at my hobby shops, but I'll probably pick a couple up for the few booklet cards I have in my collection.
You can see product information on UltraPro's website here. BCW or anyone else didn't have anything comparable on their websites.