Steve, I always love your input. It never fails to give me things to think about. The whole notion of J&P as the 800 lb gorilla is so interesting. I never noticed it, mainly because I do live within 200 miles of the Monterey Peninsula, but I'm sure you're right. For all of those years, they sold only their own roses and a selected few others, and they were the absolute leaders in terms of sales, I'm sure.
In the years before J&P and some other huge nurseries started going downhill, Wayside Gardens was another reliable source. Their rose catalog was the highlight of every rose gardener's year. It was at least four times as thick as the J&P catalog and they offered every type of rose. At least three-fourths of my OGR's and David Austin roses came from Wayside in those years. Spring Hill was also reliable in those days, believe it or not. The selection was much more limited, but they carried roses that were unavailable from J&P or Wayside. I still have dozens of roses from Spring Hill in my garden that have been going strong for 20+ years now.