Can anyone find any textual evidence that supports Ferdinand of The Tempest to be bisexual?
I was unable to find any textual evidence of Ferdinand's being bisexual. In fact, in Act III, Scene I, Ferdinand tells Miranda of all the women he has been interested in, and none of them compare with Miranda.
However, if there is something specific that you have encountered through your reading of the play that gave you such an indication, include it in a question. A specific quote can be closely examined and interpreted.