Check with treknomads, Kesari. Thrillophia offers packages. Also check with Indiahikes. A few friends once used their service and said it was good, but that was years back. Just thought of sharing in case you might look into it.
According to my personal experience.. you don't need any agency just go with some of your friends.. there is no much luxury in this trip stay in gurudwara @ ghangharia & govindghat do as what locals do just get your strong friends physically & mentally with you ... get the first bus from the haridwar to govindghat ( joshimath) stay in gurudwara there then start your treak from ghangharia to velly of flowers along with hemkund sahib gurudwara both treaks close to each other Foodiing & lodging can be done in gurudwara this would be the best plan thanks & regards