Allow me to elaborate further on why the tour service is your only chance...

Both Boca and River have huge groups of supporters, with a very large % also being Club Members and season ticket holders. This means that less than 5% of all stadium tickets are not already sold before each of these super-clasico games.

Therefore your only source aside from the tour services will be the scalpers... where you run the risk of getting fake tickets and also not properly understanding where you will be seated (if the tickets are good).... or you would have to go with the masses that are not season ticket holders and camp out 48 hours before the very few non pre sale tickets are put on sale at the stadium.... and be prepared to get only 1 ticket per person if you camp out 2 days before and have an early enough slot in the line... etc. etc.

Trust me... while the tour service will of course include a mark-up, its your best bet... they also include transportation to and from the game, and the ticket they usually get are decent.

On a final note.... just for reference, if you are lucky enough to find a scalper that has tickets to some of the best seats in the stadium for such a game, you should expect to pay approx. US$500-600 per ticket.