There is one available, the Asus Sabertooth 990FX/GEN3 R2.0:
http://www.asus.com/Motherboard/SABERTOOTH_990FXGEN3_R20/
Its kind of pointless however, as it uses a PLX chip to direct the 990FX's two PCIe 2.0 x16 slot to one PCIe 3.0 x16. So in effect its just using a PCIe 2.0 "x32" slot...
Anyway the performance increase from using PCIe 3.0 is -minimal-... we're talking 1-2% max...
AMD is apparently working on a successor to the 990-series, but with all the restructuring lately, I would not hold my breath. Its questionable if it will ever see the light of day. All AMD CPU's are likely to move to the FM2(+) platform...