I bought veneer from Constantine's back in the 80's and still have some left unused. They used to advertise heavily in the then-available woodworking magazines. Another (the only other one I knew of) source of veneer was Bob Morgan, from somewhere in KY. I had thought for a long time that Constantine's had went out of business, only to find they were still operating. I do think they may have moved from their former location....but they are great to deal with.
It's a great read and loads on useful info! I've never got so deep into planes that I worried about the "type" mine were (the Stanley planes) but it's was still interesting to go through the info.