Stop four was because I am my paternal grandmother's granddaughter. Nagano is famous for its soba noodles but it also, among other things, produces rhubarb. A quick google search led me to the Nagano JA (Japan Agriculture) website's rhubarb page where I discovered a likely source in the Shinano-machi Michi-no-eki (literally "street station," a rest stop like area that showcases local produce and other items).
Did we find rhubarb? None fresh/raw, it is too early for that, but I bought three kinds of jam, cakes (for U's parents), chips, juice, and gelato! Yummmmmm! I'm one super happy camper!