I have never looked for ear drops before, but here is some info I have found on the Web:
From http://www.drgreene.com/21_1767.html:
"Topical drops specifically for earache relief are also now available over-the-counter in the eye/ear care section at most drugstores, grocery stores, and discount superstores throughout the U.S. These drops have a long history of use in other countries where antibiotic usage is not as prevalent."
And from http://ezinearticles.com/?Ear-Pain-Relief---Quick-and-Eas...:
"If you don’t have any medicated eardrops available to use, here is a household remedy. Warm up some garlic, vegetable or olive oil and put a couple of drops in the infected ear for ear pain relief. You need to make sure that the oil is warm and not hot. If the oil is hot, you can cause permanent damage, such as affecting your hearing.
There is an easy way for you to check to see if the oil is warm or hot. Apply a drop on your inner arm to see if it is okay to administer in your ear infection for fast pain relief."
Perhaps this 2nd idea is what your grandmother used. Or if you would rather buy something from a drugstore, I would just go in and ask the pharmacist what he/she recommends.
(NOTE: I just re-read the age of your son. If it were me I would just go ask a pharmacist what is available for his age, and possibly ask the pharmacist about the home remedy.)