I wouldn't be too worried about petco/petsmart tanks.. so long as the silicone is inspected first, you don't use their stands, make sure it is flat and level and leak test before you first use it
My personal preference is for rimless tanks . But as you gave the stand built already, it likely assumed a tank with a rim.. and rimless are generally far more expensive not to mention not being the same dimensions as a 'standard' tank.
Another resource might be to get in touch with a local club, I think motor city aquarium society is around detroit, and likely gas members who can help you out with specific places to go, or maybe have a member selling a used tank. I know there are plenty of used 75g tanks by me for sale for example.
If you want to shop local, maybe try a store that specializes in cichlids or larger fish, they are more likely to be able to help you out . Or if you didn't already, talk to the owner of the store you tried.. it can be that the staff just don't want to make the effort to help you out or don't have the ability to order themselves)
As an actual standard aquarium branfmd, I would check out Seapora