Hello Mick.
By Ent's reckoning, there are 4 who remain.
Radagast,
Gandalf, and the two "
blue wizards." whoever they are, or possibly were.
Gandalf is said by most to be the only one who actually fulfilled the mission he was given.
Radagast's end is not known.
Nothing is said about the blue wizards whatsoever in the strict cannon. There may be brief remakrs about them in the 'extra-cannon writings.' Much is speculated about them, and they figure in some fanfic stuff from time to time.
That said, there are many
maiar remaining, and no doubt come could be classified as '
wizards' should they need to be interacting as so with the "children of
Eru."
The
balrogs are, for example, maiar. They are called 'balrogs' because they interact with Humans. But all maiar have powers of a kind. And if one takes a form and retains it for too long, (if Ent understands rightly), then they remain in that form.
The balrogs took and kept the forms of balrogs, so balrogs they became.
The wizards took the form of wizards, and needed to retain it for
ages, so wizards they became.
The
Ents were '
spirits from afar' who "inhabited"
trees, so Ents they became.
Here is another thought along those lines. Arguably,
The Mouth of Sauron is a somewhat powerful entity. And whether human or
maia, Ent believes we know nothing about him and what happens to him during or after the final confrontation at
Mordor's gates. What happens to him? How does he figure into people's thinking about the future of
Middle-earth? We know
evil remains, and in many forms and guises. what role do these things play?
