your best bet for those low voltages and loz currents are "voltage referance" chips/ics, most are in a to-92 case or surface mount, they come in 2 types, programable and fixed.
heres one that is so close you could use it, if it will work for your circuit. it is a .6 volt with a 6mv tollerance, so its min/max = .594 - .606

http://www.onsemi.com/PowerSolutions...t.do?id=CAT102

you can always use 2 programable VR's and create a differential voltage of .58 too.