For Boca and River you'll have to buy a 'tourist' ticket. You'll be able to do this through companies you find online or through your hotel etc........ These tickets are more expensive because every game is sold out to s/t holders so this is the only way.
I don't know if the thread is still there, but a poster on the old forum said he had a contact for getting tickets. If you have a look (if the search function is still working) then you may be able to get the name of the poster and contact him on here.
Nowhere near the same thing but you could always try some of the other clubs if you can't get tickets for a Boca game. If you get tourist tickets for Argentinos Juniors they'll give you a tour of the museum and they used to let you on the pitch after the match (don't know if this is still the case).
There are loads of teams in BA so plenty of oppertunities.
Boca have had no Continental games and all the travel; River, Lanus, Racing and Independiente have been playing reserve teams in the league to concentrate on Continental games; the likes of River, Racing etc......lost their best players in the last transfer window and didn't replace them - Boca kept theirs; etc....
Talk in Argentina that Tevez could be returning to Boca in January.
Also, Gallardo is quoted as saying that he wants to stay at River. Any decision is up to the Board. Bit of a volte face as he had indicated that he was going to leave - still think that would be the best decision.