You can get stainless steel replacements from Chris Shaw Engineering-good value and beautifully made, and wont snap as soon as you try to bleed your brakes!
I was just on here looking for the answer to this very question! Not sure if you can get them in most bike shops but I do need a nipple too, and was going to try Kennedy's in Drogheda on Monday for one....
Anybody know what size to ask for???
Do nipples come in different sizes???