I had one with ds and ended up making them for my friends because they're ridiculously simple. If you sew, all you'll need is two 15''x15'' squares of fabric, two bands of elastic (one 3'', one 5''), and a couple of buttons.
If you DON'T sew, and don't want to pay the $16 dollars, or whatever they want for them, I'd be happy to make one for you.
They work well! I remember wearing one in my pre-preggo pants at about 8 months, so disregard what they say about early - mid pregnancy.
Hey! Thanks for posting the link. I am going to make myself a couple. Just wondering about the button part, though. Do you put a button on one side and a button hole on the other side of the elastic? The pants the lady is using doesn't look like button pants. Maybe that's why I am confused?