You need to make the bus trip in two segments Hakoneyumoto (箱根湯本) to Sengoku (仙石), then on to Gotemba Station 御殿場駅).Here is the timetable for the Hakoneyumoto to Sengoku segment:
http://farm4.static.flickr.com/3243/2893178584_541067b2...
and the Sengoku to Gotemba segment:
http://farm4.static.flickr.com/3134/2892923340_2407e14b...
Good luck!