4 Spatial Stream Wireless Routers/Enterprise AP's?

I know the 802.11n specifications allows up to 4 x 4 : 4 configuration of Tx Rx/streams, but are these even available on the market today? I know iv seen very few 3 x 3 : 3 configuration routers but hardly any 4 x 4 : 4 spec ones.

Anyone know if any 4 transmitters, 4 recievers and 4 spatial stream spec AP's / wireless routers on sale anywhere on the interent??

TIA.