If by organically you mean naturally, your wife choosing to let a black man fuck her without you or anyone else saying to her how exciting it would be if she got fucked by a black man, then seems unlikely to me. I think a white wife would need to know without any doubt that her husband would support her being fucked by a black man.
I often told my wife how exciting it would be to watch her suck a black cock and being fucked by a black man but I never pressured her. My wife had already been fucked by other white men before I caught her cheating on me, so the only new parts to her would be, it would be a black man instead of a white man and I would be watching.