From the Rambam there is an understanding that there is no need for a particular species as long as the dye holds. There are, though, quite a few opinions how to interpret the words of Rambam. Are you aware of any other dye in this color family that meet this requirement and were available in the last 1000+ years?
Outside of the Murex family of snails – the only organic source for indigo dye is from plants: Indigoferra tinctoria and woad. – Mois Navon.