LOVE (and wish I had) that Dodgers/Giants pennant from 1958. What a beauty!
I can certainly see why that's rare, but others remain a mystery. As for the White 1962 Giants Champs Pennant with the rivets.... the 1961 Reds version is one of the most plentiful on Ebay. I think there were 7 or 8 nice ones, last time I looked. So did they just make far fewer the following year (in '62?)
http://www.ebay.com/itm/VINTAGE-1961...wAAOSwMtxXv2Hl
There are (maybe) one of these Giants versions for every 100 Reds.