No, sorry, the chemical wormers all recommend withdrawal of some sort in the animals they are intended for. You may get some recommendations for "natural" wormers, things like garlic or pumpkin seeds, but I would be amazed if anyone produces scientific proof that they eradicate an infestation.
Where do you live? If you are not seeing any symptoms of worms, if they seem healthy and are of good weight, their population could be very low where you live -- they usually are in desert climates, for example. They are usually worst in warm moist climates like mine. Probably the worst worm is hookworm, and they leave visible sefments in the poop that look a bit like rice.
And if you birds are really badly infested, you will probably find a roundworm in the poop sooner or later.
You could see if your vet will do a fecal float test for you, which should reveal the presence of worms if they are present in large numbers. The chances are that most chickens live with a tolerable number of them.
