So I have no personal experience but a quick google search lead me to this:
http://roperonet.com/hombres.php
Whose prices are alarming and whose styles seem to match what I've seen in 9 out of 10 rented tuxes here (usually only found at weddings) aka total train wreck.
There is a large section of corrientes between pueyrredon and callao that seems to be dedicated to this stuff. Maybe you could go for a stroll around there and check out what's on offer.