If you are OK to wake up and get off a bus running for another prefecture, one option is Hokuriku Dream Osaka 1, which is operated by West JR Bus.
: Osaka Station JR Highway Bus Terminal 22:20 -- 05:54 Kanazawa Ekimae (destined to Toyama Ekimae)
Here are two types of highway bus services in Japan: highway share-ride bus and highway tour bus.
Highway share-ride buses are offered mainly by route-bus companies. JR Highway Buses and the bus service above-mentioned in the japan-guide.com webpage are highway share-ride buses.
Highway tour buses are offered mainly by tour companies, which consign bus operation to bus companies.
frog1954: but when I searched on the web, I found the following one.
According to the website of the link, this bus running from Tennoji, Osaka via Kanazawa to Toyama will be available until 14 January 2013.
This bus service is a highway tour bus, and the profile of the offering company is found on a list (in Japanese) of members of a liaison council on highway tour bus (http://www.etba.jp/member).
It seems that this company is not a bus company, judging from that it is not appearing on a list of highway tour bus companies announced by MLIT, which the ministry began to make and publicize following a serious highway tour bus accident in April 2012.