The White House offers free greetings for special occasions from the office of the President. There are a number of restrictions, and not all greeting requests are fulfilled, but it's worth a try if you are interested.
You can make your request by fax, postal mail, or an online email form. I suspect that you are more likely to get a response if you use fax or postal mail, but that is just a hunch on my part. Advance notice is required for everything except wedding congratulations.
Some of the occasions for which White House greetings are issued include -- 50th wedding anniversary and greater, 80th birthdays, births, Scouting awards, Bar Mitzvah, Bat Mitzvah, and weddings.