Himalayan trekker
India hikes
Glacier treks and adventure
Nature wings
Bikat adventures
are some groups who organise sandakphu trek.
https://tripoto.page.link/oRsNN1LuvmsifZHy6
Kindly check the above link for info.
I went with Trekkers Of India they were best in services and safety. Being a solo female I was most safest and happiest. Go with Trekkers Of India without a doubt