I cannot find an opportunity to buy a table top as a seperate
component in the size I want or the ability to cut down.

I'm interested in a 92 wide x 28 deep x 1 inch plus "table-top" to use
as a computer desk. I plan on using it across two file cabinet pieces
I did find at JCPenney. The corresponding top listed with  is only 68
inches I believe. I'm hoping for standard white, but I'm curious about
using a stainless stell surface also if you find something or a
variety of somethings.  : )  Please ask for more details if needed.

What about a kitchen counter top from a do-it-yourself store, Ikea or the like?
Length should not be a problem, and you should be able to find a
selection of  colors/veneers with good surface quality.

Good luck, Myoarin

The quick and dirty solution would be a 4 x 8 x 3/4"  sheet of
material with a melamine (white plastic) top.
You could have it cut to size at the lumber yard and paint the edge. 
Presto, cheapest of choices.  The countertop idea is pretty good,
though, because the front edge could be a finished edge and only the
ends would need to be painted.

Of the two the second option is where I'm probably headed. I thought
of countertops for your Home Depot or Lowes, but it looked too much
like a countertop. I have two nice white file cabinets and thought I'd
be able to find something closer to my specifications without
adapting. I went to a local lumberyard (quite large) and the didn't
even have 3/4 inch plywood to try to adapt.

I haven't seen a 4 x 8 x 3/4 with a melamine top. I'll have to look
further as this sounds like the direction I would like to go...least
amount of adaptation and work.  : )