Comcast may have it online at https://www.xfinity.com/learn/channel-lineup or https://customer.xfinity.com/local-channel-lineup, or they may have included it with one of your recent bills. Check https://customer.xfinity.com/.
Service Centers should have printed channel lineups. Check locations and hours at http://www.xfinity.com/support/service-center-locations/ to pick one up, or call Customer Service at 1-800-Comcast and have them send a lineup to you.
Hello karen303, the information that (BruceW) provided is correct. Please reach back out to me here if you need any further assistance with obtaining a full channel lineup listing for your area.