I had a tie rod end fail back in March at about 120,000 miles. I did not have the shimmy sympptoms that you are describing, but it is a likely sign that the ends are failing.
If you've had two alignments and nobody has pointed out the tie rod ends were bad (if they are indeed bad) I would be pissed. That should be something that gets checked along the way. It sounds like it is the case.
If they have gone bad, consider getting an aftermarket tie rod end from Moog. They have Zerk fittings on the joint so you can grease them up. Lifetime lubed, what a joke.