Nagaden bus ticket

Hi!

We'd like to visit the Jigokudani-Koen and I already found out, that we can take the Nagaden Express Bus from Nagano St. to Kanbayashi Onsen, but I can't find, where we have to purchase the tickets.
Aren't there any kind of roundtrip tickets available?

Thanks :)
AnnaLuise

I can't find, where we have to purchase the tickets.

On board of the bus when exiting as explained here:
http://www.japan-guide.com/e/e2015.html

Aren't there any kind of roundtrip tickets available?

I don't think so.

thank you :)