His options are going to be limited, since he waited until age 70 to buy life insurance coverage.
And they're not going to be cheap. Keep in mind, if he can't pass a medical exam, he'll have to live at least two years after taking the life insurance policy out, before it will pay a full death benefit. Otherwise, the policy will payout the premiums paid into the plan. This is called, graded benefit life insurance.
That's why now may be the time for you to buy your life insurance, while you're still reasonably young enough to get an affordable rate. If you don't, then you're putting your kids in the exact same position that you are in now.
Here's how you can learn about Over 70 Life Insurance and find out how your father may qualify for life insurance coverage with no physical exam needed.