Is there any other control panel software that does the same as WHM/CPanel? I would like software close to this for my hosting company but I have found that WHM/CPanel seems a bit on the slow side and lacks documentation for a first time user of WHM.

Also where could I purchase the software?

Maybe you should wait while, because from what I know the new cpanel theme will be lighter and load much faster.

They are working on new skins and themes.