When you bought them at tractor supply there were only a few days old. I think i had mine until around 7 weeks and let them out in warm weather.(or until they develop all their feathers)
Here is a picture of our american game. I would suggest getting american game hens to hatch your eggs. Ours went broody about 3 times in only one laying season! You could probably find them at your local poultry/livestock auction.
My second choice would be silkies. I do not have any, but forums...
You can not force a hen to go broody. But if you have a chicken that does, you could put the chicks of your choice or the eggs of your choice and she will hatch them and take care of them
Your fully black ducks are Indian Runners. They will grow the same size of your White Pekins but will not get as fat. I raised the exact ones last year and they were a real joy. :)
We had the same problem with 2 baby australorps last year. We would clean their vent with a warm wash rag and then put vaseline on there. They have done just fine and have laid many eggs. :)