Yep you can eat pretty much any birds eggs (but stealing wild ones is illegal).
It is just economically viable to produce turkey eggs as they are pretty much the same size as hens, yet the turkey will require a hell of a lot more feed and room.
In some farm shops you can buy them. My local even sells Ostrich eggs, one making an large omlette for two!!!
When I was young me and my mates would cook gulls eggs and eat them on the beach, a bit salty though, I scrambled some fresh ducks eggs once, they were totally gross, good for cooking though, so I'm told!!
Ratter15 are you sure the eggs were fresh. As duck eggs have such a rich yolk (that's why they are considered good for cooking) they make delicious scrambled eggs unless of course you do not like yolks when they would presumable be gross