Well, there's a strange thing: I can't find an eligible set for 1978. Have I missed something?
Mostly I sit at my PC and search the net for decent images for this topic. It's less trouble than hefting out my albums and doing a scan. And in any case my scans are not great - you can see them in the Rhodesia 1975 post. It's much better to find a nice image online, whether a scan or a photograph.
Some sets are not well photographed online, though. I wanted to show a 1976 Seychelles set but had to make do with a 1977 set instead. The 1976 set seems scarce now. I have uncirculated sets of 1976, 1977 and 1981/2, but then again, I didn't really want to heft 1976 out, just to make some ugly scan of it.
In general the availability of superb images has increased enormously, even, I would say, just in the past couple of years. The internet is still in its relative infancy, of course.