How can I obtain guardianship of my father?

You need a lawyer, and you need to go to court. You'll need proof that your father is incompetent to make his own decisions, and that you will be a suitable guardian. I understand the legal process is expensive, but I have not gone through it. Many people on this forum have been through it and can give you more details.

Could you explain just a little about why you want guardianship? That may help the answers be more specific.