sam4321– we actually do have a mesora from the chavos yair and the yaavetz as I pointed out earlier.
But either way I already pointed out the lashon of the Maharil in teshuvos siman 5 and the radvaz etc. that all say clearly it is possible to find it. What this taaneh that you need a mesorah probably means that it needs more than to fit with the simanim. The radzhiner techeiles had no rayas at all, rather it just ”fit” with all the simanim of chazal. The yeshuos malco said about it ??? ??? ????? ??? ?????? ????? ???? (??’ ??”? ?????? ???? ??’ ?). So for that the Bais haleivi said you need more of a mesorah. However, the Murex has loads of strong rayas and is not just a guess. When the Chazon Ish was asked about his esrog which had no mesorah, he said He has so many rayas it is better than mesorah.