This question is coming up more and more as members of the "sandwich generation" deal with aging parents. You can buy life policies on your parents almost anywhere.
In most cases, the parent you are insuring will have to give consent to be insured by signing the application. There are a few cases where you could take out the policy on them without direct consent but, to do this, you would need a formal "Durable Power of Attorney". Carriers that allow you to sign as POA, are usually guaranteed issue carriers so make sure you know what you are buying.more