I did some research on database sites plus a bit of googling and found two leads.
- On some servers Life Force Pots are sold from the merchant in the Alchemist's Guild and are used as an ingredient to make Embryos. I went to this merchant and he doesn't sell them on iro.
- In the Kafra shop there are "Small/Medium Lifeforce Pots" for sale. Surely these can't be the items for the quest because that would be stupid.
EDIT: Mystery solved! These are in fact sold by the merchant in the Alchemist's Guild but are called "Glass Tube" instead of Life Force Pots. I was able to complete the daily quest with these.
Edited by Blueflight, 08 August 2011 - 01:12 AM.