[TowerTalk] Need for a LM470 sheave(pulley)

[K6QD]

I need to replace a sheave (bad roller bearing) in an LM470.  It is an older
Tri-Ex and the sheave is an ATCO M4-6B (no reference to ATCO on the
Internet).  It's the one at the top of the first section that the pull-down
cable runs over.  The bearing is a SKF KR6 (no longer mfg'd by SKF and no
x-ref).  It appears that the bearing is simply pressed into the sheave and
would be replaceable by itself.  So, I'm looking for sources for either the
entire sheave ass'y w/ bearing (preferred) or just the bearing.  The sheave
is 3.5" O.D., 0.5" width, 3/8" pin bore and accommodates 1/4" (or 3/16")
wire rope.  
Karl Tashjian is looking into it.  His replacement sheaves are expensive.
Tks!!   Mike K6QD