Classic episodes of Doctor Who can be hard to find on television. I recently discovered a channel that shows Classic Who almost every day. It's called Retro TV. I'm not sure when I got this channel, since I'm normally only looking at the HD channels in the guide. I discovered it by accident when I was searching for Doctor Who in the Tivo search. There it was, down in the low numbers, right near Create.
There's an hour of Doctor Who on every weeknight. Right now they're showing the 4th Doctor. On Saturdays, there's two hours! That's at the end of the 7th Doctor's era now. Check it out!