No, you can't put 700c tires on 27" rims. And I'm not aware of any 27" knobbies.
If you have a bike with cantis on it you MIGHT be able to fit 700c wheels on it though. A road bike converted to a cross bike might not have a lot of clearance for knobbies and it can become a problem in mud.
But I converted a Gitane Tour de France into a cross bike by adding canti bosses and doing a rattle can repaint that worked nicely except for the mud clearance problem.
Rattle can paints generally are too soft and scratch easily but you can sometimes fine a clear topcoat that gets hard enough to protect the paint.
For knobby 27" tires, check thrift shops that sell old bikes. You can sometimes find an old 27" wheeled bike with knobby tires for 75 dollars or so. Maybe replace the tires with nashbar cheap-o's and re-sell the bike on Craigslist. Now that I think about it, that's really a long-shot.
Used to be you could find 27" tires in department stores and sporting goods stores that sold bikes, but that's getting pretty rare now.