How to find network by channel

I am so frustrated.  I want a simple list that tells me which network is on which channel.  I cannot find it on the Comcast website.  

How hard should that be?

For example, I want to watch a baseball game on MASN.  What channel do I choose?

Or I want to watch David Letterman on CBS.  What channel do I choose?

This is basic stuff and should be readily available, but I can't find it.