I see you have no responses here. Maybe a lack of people from Detroit and I can't help with a specific store either.
I have ordered mine online, through Craigslist, or through another Lemons team. If you are worried about size, for most brands there are basically 2 sizes; normal or wide. If your 6'6" guy is wide there is your answer. If not then there is also your answer. Most seats when ordered can be had with sliders often times with mounting brackets that can be car specific if you run a car that is frequently customized. If you go to your local autocross, Lemons race at Gingerman in June, drag strip, or most any race oriented car event you will likely be able to talk about seats with guys there and try them out. Then order what you liked. For a tall guy the biggest thing is sliders and seat placement. Most seats are fine for a 2 hour stint. I've really liked my Corbeau's.
Team Glue Sticks
00 Firebird, 02 X-Type, 93 NX2000, 00 Mazda 626 (Sold)
2016 NJMP Heroic Fix, 2017 NJMP Near Heroic Fix except we can't drive, 2017 Thompson I Got Screwed, 2019 Pitt Heroic Fix