'CA' glue is cyano acrylate or Krazy glue.  I don't know how it works on
ivory keytops.  I think it would only work to replace a top from its
original position, with little gap to fill.  Using the heavy bodied stuff
would probably make a sloppy mess.

I have used both ivory cement and wafers.  Since ivory is translucent,
I think the important thing is to use the same method as originally used
on the piano to minimize the color difference.  I also agree that small
chips are better than color and grain mismatches.  Old ivories are also
often worn and may not have enough thickness to match in with the
remaining tail.  Then there is the fact that different notes have
different bevels.  Different sizes, and trimming and beveling or rounding
techniques were used.  Original grades and colors and even species
(elephant and I believe Walrus) were used.  Yellow can be bleached out
with industrial strength hydrogen peroxide and sunlight.  It can also
damage your skin and leave the keys porous and dull beyond the ability to
polish it again.  It's too bad that old  pianos didn't have extra ivory
sewn onto the tails, as the better shirts do.

In summary, if you have near perfect ivories with just a few missing or
broken, you might be able to match them, but it won't be easy.