If you need them drilled through, there is vise available to hold
it and line it.
It is simple to make a 'vise' to hold any spherical object for
drilling - just take a length of metal such as brass, say 1 inch
wide, 1/16" thick and maybe 6 inches long and, near each end drill a
hole which is about half the diameter of the ball (pearl) you want to
drill. Countersink these holes and file away any rough edges, then
fold the metal in half so that the countersinks face each other and
the holes line up exactly. The ball can now be held between the holes
by the springiness of the metal while it is being drilled or, if
necessary, the whole thing can be held in an ordinary vice.
Ian W. Wright