jplacson...this thread is a perfect showcase as to why piece mealing a front suspension is problematic. Shimmy as mentioned is a function of really everything. Yes the thrust arms are the biggest contributor but everything has to be in relatively good condition to mitigate vibration. Sounds as though you replaced your thrust arm bushings but not the thrust arms themselves. Now you have to go back in and replace the thrust arms if you want to quiet the vibration. Then there is the lower arms and the tie rods etc etc. Everybody wants a silver bullet to conserve cost. At the end of the day you end up spending more by increasing the labor cost of going in each time and chipping away...reality is everything has to be in pretty good shape for the suspension to work properly. There isn't any magic to getting rid of shimmy.
Good Luck,
George