There is only 1 durect train from Chandigarh to NJP, TRAIN 15904..Avail that to reach NJP and from there you will get ample car/shuttle jeep to Darjeeling.Midway between Siliguri(as you have to avail car for Darjeeling from Siliguri which is just near NJP where the train will drop you) and Darjeeling is Kursheong.From Kursheong you may avail Toy Train for onward journey to Darjeeling.Hope this helps.Have a pleasant stay in the hills