Dont go to Kalka, alight at Chandigarh, from Chandigarh (ISBT, Sec - 43) the ST buses are available 24 hrs for Manali, appx time 9-11 hrs on NH-21. ISBT-43 is appx 7 kms from Chandigarh RS.
Otherwise on rail Route, nearest railhead will be Kiratpur sahib between Rupnagar and Nangal on the Morinda - Una section. from Kiratpur sahib, the distance by road is 240 kms, where as from Chandigarh its 300 kms.