It's next to tempe town lake basically. Just go south on scottsdale rd, west on the first turn south of the lake(west rio salado parkway), and south on the next turn(s. mill ave.). Mills End cafe is at the intersection of W. 3rd st. and s. mill ave.
cant come to this jam personally, but i will definitely be there next time.
btw, free parking is at any of the tempe town lake parking areas. instead of going south onto mill ave., keep going west and they'll be parking just north of rio salado west of mill ave.