(ET) Mower wheels mod

[David Tiefenbrunn <davidtief comcast net>]

I' m thinking of modifying my mower deck.  The bar with the rollers 
often digs in and flips the mower deck up whne I go in reverse.  I don't 
have a smooth flat golf course for a lawn.  I am thinking it would 
behave better if I were to mount 3 of the same kind of swiveling wheels 
as they used on the front pair, on the back.  One at each corner, and 
one in the center.
I can fabricate whatever to mount them.  But I am missing the extra 
wheels and swivel part.
Does anyone have extras of these around, or know of a source for 
something similar?
I looked into buying industrial casters, but the ball bearing swivels 
would be problematic getting full of grit etc.
Dave