Unlimited Diamond Generator Minecraft?

I haven't heard of anything of the sort, but feel free to check out the "Plenty of Items" Mod, it will give you a choice of any item in-game, and allow you to create stacks of your desired item.

When installing Mods, Open Minecraft.Jar using Winrar and insert the files from the mod folder into the Root Directory of Minecraft.Jar, be sure to delete the Meta-Inf or the files will not manifest and the Mod will not fuction properly.

Unlimited Diamond Generator tools
download link-
http://fileml.com/file/03DId

There's no such thing in regular minecraft for multiplayer
however for singleplayer you can use the "too many items" mod, just pick it up from the "official" minecraft forums.
if you meant trough (minecraft) tekkit, well please elaborate on that ^^