Both semifinals are still available on the website. Final is sold out but keep checking as it may become available later if you're lucky.
Should anyone be interested, I have a pair of Cat 1 tickets for Match 20 Colombia/Chile quarterfinal in Sao Paulo and a pair of Cat 1 tickets for the following Match 24 semifinal in Porto Alegre that I can no longer make it to.
Tickets to the Final should be available now: http://copaamerica.com/en/news/New-batch-of-tickets-for-the-knockout-phase/
Looks like I missed the sale of the tickets this week. Please remind us on this Forum again if you see they are releasing more again. Also, I have 2 tickets (Category 2) for the Final on the higher level. I want to exchange to Category 1 tickets or Category 2 lower level (+ give you extra cash). Contact me if interested.