There has been much debate about the blue dye (techelet) for one string in the tzitzit. Here is an interesting article for thosewho may want to learn more.
I am able to supply these tzitzit (at an additional cost of $25) but the synthetic type is recommended so that the dye does not rub off on your clothing!
If the blue string is simply symbolic, I can dye the shamash string to a shade of blue very close to authentic.