they try this just about every year.
no one knows for sure which fish to get the right color from, though there is a majority opinion, its not conclusive nor would it be accepted for use in a future temple.
BUT some orthodox jews do use what most think techelet is on their regular fringed garments that we wear all day under our shirts.
Not that it affects the commandment to wear them and by wearing the tchelet some are right while those not wearing it are wrong, just a little 'over and above' to show that they're trying hard to follow lette rof law which says fringes should have tchelet.
BUT all jews are absolved from wearing tchelet on our fringes till teh time of temple, so moot point, just done for glorification of the act.
(all of these terms are RELALY weak english translations of hebrew legal terms... no good way to phrase them!)
also, its very easy to prove you're a descendant of aaron. IT's been passed down whether you are a cohen (priest - perform temple service), levi (kind of like temple maintence and caretakers) or yisroel (normal jew)
kohen = son of aron, levi= rest of the descendants of tribe of levi (aaron is from levi, but only his kids are priests), yisroel = everyone else
so if you are a kohen (last name usually Cohen, or Katz which is really an abbreviation of two words
kohen
tzeddek = "righteous priest" - K+TZ = Katz) then you are a son of aaron, no doubt about it. categorization is passed down paternally too by the way.
AND, these people making all the 'tools' for the temple are viewed by most orthodox jews as just wasting their time. None of this can be used as the world exists in a state of impurity now and nothing made in such a state can be used in the temple. For example, they made a menorah to perfect specs. I saw it guarded by more people than the PM when I was in isrrael, proably 3-4 tons of pure gold. BUT menorahhas to be made out of one piece of gold jsut like aaron did and it's impossible for the hands of man to do it that way in the correct fashion.
ALSO the tools and clothes from teh temple were not detroyed nor could they be for that matter. all of my people know where they are and when the time comes we'll just bulldoze the vatican and get it all out of the basement. not kidding bout that.
ETA: thes people aren't doing a bad thing. They're not like the whackos who try to get ontot the temple mount to pray once in a while. BUT they are wasting their time and money.