Try taking a clear plastic bubble, coat half of it with black paint and put that on a hook. You have to slide them over the hook eye. The bubble is more oval than round. I put a couple of legs on the front with some dubbing to hold the bubble on the hook.

I found some a few years ago that were black on one half and silver on the other half. They worked great in the ponds in Colorado.

Now.... If I could remember where I found them. I don't even have the tags for the packages, plus, I've lost all the flys or they were destroyed by fish..