Oh! I hope you will come back and post about the making of the two (mix-media?) paintings!
With so any options for pearl shapes, colors, sizes... around, I have no doubt you will find a suitable one.
Have you considered blister (mabe) pearls? For once,
the typical half-pearl shape given to most cultured blister pearls is perfect for fitting on a flat surface (=canvas) and sometimes flat nacre is left around them and the resulting object looks as if a round pear was rising half-way from the nacre around it... although that has nothing to do with the way these pearls form, of course. Take the
abalone blisters or
the black ones, for example.
Blister (mabe) pearls are usually both larger and cheaper then full pearls.
A similar argument goes for button pearl - whole pearls that have a flat side.
Just a thought...