There are no flights to Kalga. From Delhi or Chandigarh there are buses to Barshaini village. From the village you could get a lift or a shared safe ride to Kalga. Many suggest walking for Kalga is half an hour away. Another way is via train till Pathankot then take the bus that routes to Bhuntar one such stop is Kalga.
To lay it out simple arrive in Delhi from your place of stay reach Majnu ka Tilla or kashmiri gate book a bus via Paytm or redbus i would suggest Malana travels or any other with high rating, if you take the 5:30 pm bus you will reach kasol at 6-7 in the morning.
local buses start around 9ish or you can take a cab which run on union prices (700 till barshaini bus stop) i would suggest the local bus which is much cheaper 50-60 bucks after arriving at barshaini bus stop you have to walk till the Dam from there one route goes to Tosh and one to kalga ask any gaurd near the dam for the stair to kalga it's right near the dam.
From dam it will be a small hike to kalga.