I think Hobby Lobby stocks that one.. but if you look at the photo, you can make one yourself.
The trickiest part is the release. I wrap a rubber band around the fuselage of the glider held by a trigger on the servo arm. The whole thing is released at once.
I had to add braces out on the wing of the carrier plane to keep the glider from tipping in turns.
And... the glider CAN affect the way the assembly flies... it's controls still work when it's on the cradle.