Since you already bought the diaper, you may as well give it a shot without any booster pads and see what happens.

One would hope that the "standard" (no boosters) absorbency would be good for
something!
Besides Babykins, you can get adult-sized cloth booster pads from Changing Times, Dependeco, Snap-EZ, and a few others. If instant gratification is your thing, though, you can probably find a Babies 'R' Us or a maternity store in your area that sells cloth diapers for babies, and specifically prefolds. I use baby prefolds as boosters all the time. You just fold them in thirds, width-wise, and lay them in your adult diaper. They're a bit shorter than most purpose-made adult booster pads, but they work very well.
I've found the common Bummis, OsoCozy, and Gerber baby prefolds in maternity and baby stores near me, and any of those diapers would make a fine booster. My favorite booster diapers, though, are the bamboo baby prefolds from Green Mountain Diapers -- SOOOO soft! But those are an order-online thing.