There are no direct buses from Rishikesh to Munsiyari. And in fact, the route from Rishikesh to Munsiyari is quite long, as Rishikesh is considered to be the gateway to Garhwal Himalayas, while Musiyari lies in Pitthoragarh district of Kumaon division. So, regions like Almora and Champawat are closer o Munsiyari. You can hire a taxi from Rishikesh and reach Munsiyari. Or, you can also board a train from Rishikesh to Kathgodam, which is the nearest railway station to Munsiyari and then take a taxi from there.