Hey Akshay, Lanjophaka in Thimphu - 97517111808 Knight motors in Thimphu .... Bhutan T.U.S.K motorcycles ... You can also rent motor bikes in Siliguri and Jaigon in West Bengal in India and then ride all the way to Bhutan .... Happy Riding and Happy Travelling!!!
You can easily rent bike from Siliguri as well Gangtok too. Gangtok is costlier than silliguri. But u will need inner line permit from gangtok or Rongpo.