Here is what I could find........check out th links they may give you a more in-depth idea as to what you are looking for.
1)Variety the Children's Charity of St. Louis has been doing telethons for over 3 decades
2)Jerry Lewis MDA Labor Day Telethon was first televised in 1966 and raised over 1 million dollars .
3)The United Cerebral Palsy telethon ran from in 1950 through the 1980's but have now found other means of raising money through their website.
4)The Green Bay Cerebral Palsy telethon is supposed to be the longest continuously running telethon - broadcast the 1st week in March
it was started in 1954 and is still running today(2008)