Sickle bar mower
 

Ok simply put, how hard are they to find and how expensive!

They are not hard to find, but the money is to buy one.

Sickle bar mowers are pretty scarce. Trying to find one that is designed to fit a Cub Cadet can be tough.
Haban made several models that were specifically designed to fit Cubs. The company is no longer in business so parts are nearly impossible to find.
If and when you find one, you can expect to pay $300 to $500. Even then, they may not be complete, so getting one up and running can be a real challenge.
Do a Google search for Haban Sickle bar mowers, you'll find more information.

About the only ones I have seen have not been for sale and were purchased for $500 or more.