Purchasing highway bus tickets

Where can I purchase the overnight highway bus tickets in Tokyo. I've heard that the "Midori-no Madoguchi" offices don't sell tickets for some of the routes, so where else are the tickets being sold? Also, are Sunrise Izumo and Sunrise Seto the only overnight trains between Osaka and Tokyo (not including the ones that are already discontinued)? If not, what else are available?
Thx!

"Where can I purchase the overnight highway bus tickets in Tokyo. I've heard that the "Midori-no Madoguchi" offices don't sell tickets for some of the routes, so where else are the tickets being sold?"

As for the routes run by JR affiliated bus companies, you can purchase overnight bus tickets at any JR ticket counter. However those operated by some other companies, you may need to go to the bus depot the bus leaves from or to a major travel agencies such as JTB to purcahse the ticket, though it may incur a premium for the service.

What route(s) do you have specifically in mind? As for Tokyo-Osaka scheduled bus routes, a majority of them are run by JR Bus companies.
http://www.jrbuskanto.co.jp/bus_route_e/

You can book a seat online with this tour bus organizer.
http://www.123bus.net/

"Also, are Sunrise Izumo and Sunrise Seto the only overnight trains between Osaka and Tokyo (not including the ones that are already discontinued)? If not, what else are available?"

That's the only overnight sleeper train, and still less, the Osaka bound service doesn't stop at Osaka. The first stop from Tokyo or Yokohama is Himeji.