Tires: low profile flat tire: fix or replace, toyo proxes fz4, freeway speeds

Question
After driving approx 0.1 miles, I discovered I had a flat due to a nail in the center of the tread.  I drove the car back home and put on the spare.  The tire is a Toyo Proxes FZ4 @ 245/45R17.  The tire shop that fixed the tire said that the side wall had been damaged and that I should seriously consider replacing it.  When I inspected the inside of the tire, you could see where the rim had ridden. It was smooth and slightly discolored (lighter than the surrounding tire casing), but it did not look severely damaged to me.  There were no large chunks missing and no cuts evident on the inside or the outside of the casing.  There was a substantial pile of rubber dust in the bottom of the tire; about the amount you could hold in your cupped hands.  I suspect I know where I picked up the nail, so I think there is the possibility that I could have driven as much as 6 miles on the tire at freeway speeds as it deflated.

Replacement with the same tire is not an option since the FZ4 has been discontinued.  I tried the local tire stores and the internet guys, but my size is not available in this tire.  Did find a used tire online, but that kind scares me.

So, use the fixed tire or replace it with a comparable, but unmatched new one?  What would you suggest?

Answer
First, the rubber dust came from the air retaining part of the tire, so some of it is no longer there to hold in the air.  This is not good.

But more importantly, running a tire underinflated, especially at the level where the rim leaves a mark on the inside, can damage the structure of a tire in ways that are undetectable.

So replacing the tire is the only prudent course of action.

I agree - a used tire is a bad idea.  They should only be used in an extreme emergency and then removed ASAP.

There are plenty of other tires available in your size.  

It is always a good idea to replace all 4 tires if you can.  However, at a minimum you should have the pair of tires on a single axle the same.

What I would suggest - if replacing all 4 is not an option - get 2 tires and save the old, odd tire for later.

Hope this helps.