Comcast may have it online at https://www.xfinity.com/learn/channel-lineup or https://www.xfinity.com/support/local-channel-lineup/, although the format is far from ideal for printing. A lineup may also have been included 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.
The link to the "local channel lineup" does have a "Print" option in the upper-right. It formats it as 3 columns. Mine came out as 3 pages long. It looks like this when I had it printed as a PDF, then opened in Acrobat: