There are many festivals in Sikkim and Hidden Paradise Adventure Tours can take you to them. Below is a list of them and there dates
Lepcha Festivals:
Phang Labsol (Aug-Sept): commemorating Sikkims deity Mount Khangchendzonga as well as the Lepcha-Bhutia Brotherhood pact
Loosong (end of December):Sikkimese new year and harvest festival
Buddhist Festivals
Lossar (Feb-March): the Tibetan new year celebrations with lots of food and drink. a very important and lively event
Saga Dawa (end of May-early June): this festival marks the birth, the enlightenment and the parinirvana of Lord Buddha, it is marked by monks carring scared texts around the towns streets
Drukpa Teshi (August)
Lhabab Duchen (End of Oct-Nov) : this marks the celebration of Lord Buddha return to earth.
Nepali Festivals
Dasain (Sept-Oct): a 9 day festival commemorating the family and community ties, it is also a time when the goddess Durga is given offerings and sacrifices
Tihar (November) : the festival of lights, candles are lit inside and outside to make the night as light as day, this is a festival that celebrates not only Gods and humans but also animals that have close relationships with humans like Cows and Dogs