Take platonism to be the view that there are abstract mathematical objects which exist independently of us as mathematicians and our language, thought, and practices.
Looking at the Stanford Encylopedia of Philosophy's article on Platonism in the Philosophy of Mathematics, which offers more or less that definition, it is notable that we don't get any straight quotations from mainstream mathematicians expressing some commitment to platonism.
Yet it is often said that many mathematicians incline to platonism (when they have any 'philosophical' view at all). The great G.H. Hardy is quoted as an exemplar:
I believe that mathematical reality lies outside us, that our function is to discover or observe it, and that the theorems which we prove, and which we describe grandiloquently as our ‘creations’, are simply our notes of our observations.
Now, I'm not interested here in discussion of whether platonism is right (inappropriate here!). Rather, my question is: what telling quotations from more recent well-known mathematicians could you offer students, giving other examples of explicit endorsement by working mathematicians (as opposed to philosophers) of some kind of platonism?
"Platonism" is an awfully unfortunate naming that is unfair both to Plato's philosophy and to the intended view of the mathematical world and distorts the perceptions of both of them.
I don't think a mathematician's self-image does not differ radically from a physicist's, albeit working out her way in a different universe: Inventing methods and techniques, finding out relations, sometimes introducing objects, sometimes discovering them.
Hence, I suspect that it is quite a hopeless endeavour to come across interesting examples of explicit endorsement of "Platonism" (as used by many philosophers of mathematics).
Notice that G. H. Hardy somehow felt the need to justify his art -overwhelming majority of the mathematicians didn't and don't. Why did he? I don't know; but I observe that he was a man of an era when science and technology had begun to employ enormously sophisticated mathematics.