This is the most secure thing around but you still need to caulk or otherwise seal the top
http://www.buildmartstore.com/retrospin.html
This is the only source I know of.
I have seen small storm collars with a slip-fit join on one side. It opens up to go around the pipe and slips back together at the opening. Those should be available at a local plumbing or roofing supply house.
There are also many fabric wrap then brush on systems available but they can't possibly be as durable as metals.
Good luck!
Whatever you do, post a pic and let us see what you come up with