I'm not an organic grower, but I like Alaskan Fish, Bat Guano, and Greensand for N, P, & K respectively. Rock Phosphate is cheaper than guano for P as well. Kelp/seaweed products are popular for micronutrients. You can also buy beneficial bacteria/fungi.
www.fungi.com and
www.kelp4less.com are good sites to at least window shop. Local retail outlets might carry some of the same stuff. amazon has a lot, too.
The people on here who report the best results in small spaces like yours typically incorporate massive amounts of organic matter of some kind. It feeds the good bacteria, and if you get enough of them thriving, your NPK levels don't matter as much.