Are you looking through Thunderbolt? You can do it on your model with 2 Thunderbolt displays according to Apple Support document;
Thunderbolt-capable Macs, with discrete AMD Radeon graphics can support up to two connected Apple Thunderbolt Displays.
Two Thunderbolt display
Here is a third party that does it also;
Matrox DualHead2Go DP Edition or TripleHead2Go DP Edition. Pricey though.