@patur aval assur
My Rebbe, r. Schachter says that the pshat in it comes up once in 70 years means it washes up on shore and you don’t have to dive for it, but you can get it all the time. In terms of mesorah It’s not clear if we lost the source of the dye or the process of making the techeiles [seeing as blue dye was banned]. If we didn’t lose the source, there shouldn’t be a problem to start wearing it in 5774