Missions are a good source. It helps if you have good reputation with the faction (preferably all the factions) at a station as they offer higher value rewards if you're allied. If you get the right mission, the reward can be 20 datamined wake exceptions. I use missions to keep my stocks topped up.
Alternatively, you can find one of the data harvesting POIs, such as Jameson's Cobra at HIP 12099 1B, and cross-trade the G5 data you get (adaptive encryptors capture, IIRC). Obviously, the materials traders are sharks and the trade rate is poor, but it's a reproducible, reliable way to get the data you need.