There are lots of places over there that sell tickets. Hotels, restaurants, every other shop sells tickets. Just make sure you buy from a reliable, reputable place though.
We've always bought our tics before we go but weve never seen any real queues at the parks to buy tickets though. We've sometimes bought vouchers rather than real tickets in the past because that was the cheapest option, but that was no hassle in getting the tics there. As mentioned, Downtown Disney sell tics - i would buy from there if not the park gate itself.
2000 Orange Tree Villa 2wks / 2006 Eagle Ridge Villa 2wks / 2009 Windwood Bay Villa 2wks / 2010 Ramada Gateway 2wks / 2011 Disney Caribbean Beach/RPR 2wks / 2012 Disney Pop Century/AllStar Music/Hard Rock Hotel 2wks / 2013 POFQ 16 nts