Ag, I am VERY rusty in YS. Haven't played in several years.
Anyways, I do know that Black Yoshi is in 2-1 and 2-4, and White Yoshi is in 3-2 and 3-3. I know for a fact that the Black Yoshi in 2-4 (You swing across a lot of vines) and the White Yoshi in 3-3 is easier to get. (You go down a pipe near the end of the level.)
About the other 2, I don't see why you'd want Green Yoshi back ... But I think you need to find a White Shy Guy or something like that. Don't ask me how or where, I am a far bigger YI fan than YS.
And what happened to your post? What's with all the symbols? Kinda freaky, actually.
Everyone has their own opinions, no matter how WRONG they are.