You can find a clue at the Steel Tech lab on Uveto (by, you know, talking to the guy there) but it's optional and only saves you some money on the actual resolution.
If you were already told in-game to get the 'taur samples, that means you already found the actual "solution" - Lumi, on Tarkus. If you just read about the three taurs on the wiki/forum/discord: You need to run around on Tarkus (in the wild/the spaces where encounters can happen) until you run into her, and ask her.
For the 'taur samples, you just need to find as many four-legged characters as you can and ask them for blood samples. There are plenty around, it doesn't have to be anyone specific. If you get more than three, you save some money later on.