I just got done doing a little skulking around. Here is what I could find:
-- FA has a Celery; but it is oil-based, so that is a no-go for me.
-- FLV has a Lovage Root. It is described as a "celery-like" root, with "green" vegital flavors. It is available from BCF ($5.49/15mL), and NR ($3.29/15mL). I did not look further.
-- NF has a Celery(organic). Available at DIYFS ($1.95/10mL). I don't know who else carries NF concentrates.
I think I am going to have to try both the FLV, and the NF, the next time I place an order. Now, to see if I can find a Worcestershire concentrate....