I'm not sure about the availability, but you could keep dats with oscars. I have them together...just keep in mind that the growth rate of oscars is MUCH faster than a datnoid, so you're better off getting the oscar when the dat is a little bigger or looking for a larger datnoid.
Another note, oscars put a strain on the bio-load, so you'll have to increase your water changes to keep the water quality high for the dats.