Hey Mousami,
Best colleges for B.Com(hons) in Shillong are the following ones:

1)CMJ University
2)North-Eastern Hill University - [NEHU]
3)St Anthony's College
4)Synod College
5)St Mary's College
6)Umshyrpi College
7)ICFAI University
8)Union Christian College
9)William Carey University - [WCU]
10)Shillong College

You have satisfied the eligibility criteria and you can apply to these colleges for Bcom(hons) course.Rest depends upon the faculty and the cutoff list of the colleges.
You can access this link for the list of the tentative colleges you have chances of admission
http://www.careers360.com/college-predictor

Best of luck!