missing saddle

For the very first time in a very long time I had time for a bicycle ride, so I went to get my bicycle out of the garage and quickly noticed that someone had stolen the saddle and seat post! Does anyone know where I can get a seat post that will fit a 1984 Diamond Back Trail Streak? My documentation says the seat post is 26.6 mm but when I purchased one of that size it did not fit, it was the same size as the hole it should slide into.