sb, I think you might be right. Imagine my surprise to note that I don't have any of these either and I scan everything I see...hm. Will check tonight, but basically, my technique is as follows just for the record...
Head to a system with large population, billions, any system will do. Accelerate to at least 30C to allow you to 'sense' most of the ships around you (your sensor range in SC is limited by TIME, not distance, not a lot of people know this!), then literally, go through available targets, face them, scan them. Combat/Authority ships definitely give general data more often, this is a very common type, but there are also other common types that are gained by this method so if you don't have much luck, keep going it's just unlucky that this data type didn't spawn.
Currently have a grand total of 2. One picked up on the 14 Jan, the other this morning. Both as a result of mission rewards. They certainly seem to be rarer than expected. But they do exist
That would indicate a bug, as they can be found from ecnoded emissions USS, scanning ships in SC, AND mission rewards. Judging by the fact that I don't have ANY (that's just incredible), unless I recently dumped them for some reason and forgot about it (possible). Again, I scan most ships when I'm in SC and would expect to have a large stock of these.