First off, don't buy any of the crap off eBay. Lots of people here will attest to that. Cheap and poor quailty.
Second, still have air ride? If no, then you can use same year Tbird uppers. If yes, you need to get them for a Mark for the ride height sensors.
Third, if you want OEM get out the big checkbook. As far as aftermarket, I use TRW/MOOG. Used to be 2 separate companies but merged as 1. Both companies had/have very good track records with quality.
Last, do you know if/when the lowers were replaced? Once you get new, nice, tight uppers in, it will put all the stress on the lowers. If there wore out now, be ready to replace them soon. Also could affect your trip to the alignment rack.
As far as online, you just need to shop around for the best deal. I have used
rockauto.com for a lot of parts and always got good service. Plus I have a discount code, 13517261161928, that will get you a 5% discount. Should cover shipping. Just put it in the box that says "How did you hear about us" on the shopping cart.