You could call and ask them to send you one but they charge for the shipping.
You could go to the nearest local office and exchange the modem. But there are no guarantees that you will get the "newest" Technicolor modem. They usually give, or send out, what is on hand. You could even get a older, and different, make of modem. Happened to me in the past
If it is not a phone modem you could purchase your own and eliminate the $7.00 modem rental fee. When I bought mine prices were between $79.99 to $89.99. Pays for itself in a year or so with rental money you save.
If you use a phone modem not all markets allow you to purchase a modem.
This site shows the modems Comcast generally uses.