"Bill" is also known as an ojitchi.I have had 2 before and I'll explain how to get him. (I discovered this myself when I was experementing with my tamagotchis).
You have to make a femlae tamagotchi and a male tamagotchi evolve into old timers. Make sure that you say "No" to the matchmaker everytime she comes. They will become old timers when they are 10 years old. Make your 2 old timers get married. When they leave, you are left to look after their tama babies. Instead of the tama babies evolving into normal tamagotchi children, they will evolve into ojitchis.
-sk8er girl-