Must say that anvils are very popular tools these days and here is mine, which I 'made' 35 or so years ago.
Drilled hole in my great grandfather's workbench (which is by the way full of worms and more than 120 years old
but it's made of oak and still solid.) and inserted exhaust valve from auxiliary engine of some small ship.
Head diameter is 100 mm and that's more than good for all my hammering jobs.
I don't make horseshoes, nor anything similar for which I need strange shaped anvil.