Where and how to purchase Yumeguri Tegata spa pass?

You can get to Gero Onsen by first taking the Shinkansen to Nagoya (about 1 hour from Shin-Osaka station), and then taking the Takayama Main Line Wide View Hida for 1.5 hours. http://www.gero-spa.or.jp/lg_en/

You can buy the Yumeguri tegata at some ryokans like Yumotokan, Tenryukaku, Masuya, etc. in the Gero Onsen area.