Hi Mohsin, I would suggest you to take the risk and travel the Parvati Valley in the monsoon season as it's absolutely breathtaking out there during this time of the year. Make sure to be safe and carry as much supplies as possible including umbrellas and raincoats to avoid any delay in the schedule or to avoid getting stranded. As for the accommodation part, you can check out Booking.com app where you can find beautiful homestays in Manikaran, Chalal, Rasol etc. Have a safe and trippy journey mate!
Hey, I can send you a contract number of a guy who stays there in that village of Kheerganga only. He's into this business of arranging stay and food for tourists. He was a great support when we went to Kheerganga at the time of immense cold in late December last year!
Won't recommend going there during monsoon as there are a lot landslides and floods. Not at all safe. If you do, however, want to experience rainy days there, you can go there on the onset of monsoon, but not at all in August-September.