This is not the best time of year to be looking for wild discus. Not many are collected during the high water period. Remember the seasons are reverse in the Southern hemisphere and it is the rainy season down there.
I know where some large green and Heckels are still available but they are seven inches in diameter. I'm sure they are hold overs.
These are at http://www.somethingsphishy.com
Another possibility is http://www.aquatechnics.net
although I haven't checked to see whether Alberto has any available.