I wasn't around in '89 so I'll take your word for it...but everything that I've seen seems to indicated that Agassi debuted the Hot Lava ATC IIs during his first match against Edberg at the Year End Finals (which would have been in November of that year.)
You said that this was in August of 1989. Is it possible that this was August of 1990?
I'm pretty sure that Agassi didn't switch over to the 3s until the 1990 US Open.
I would think that most retailers would have had the shoes in August of 1990 but probably not in August of 1989 since Agassi was still using the ATC 1 at that time.