re: looking to purchase modem now

i am here because i need recommendations on any legitimate online sites to purchase the particular modem model listed below. i do not want to buy from third-party sellers on Amazon as i've heard reviews of peeps purchasing stolen or equipment actually rented by Comcast and re-sold, unbeknownst to Comast and/or the third party seller.  i want to purchase this particular modem because it is the exact model i have been renting and i only get 200 mpbs speed with my comcast subscription...

Xfinity Wireless Gateway

Cisco DPC3941T | Model number: DPC3941T    

thanx in advance everyone. 🙂