Neon Green Relish
I've never found that relish in any store in the greater L.A. area, and I've looked. I brought some home from a trip to Chicago some years ago, and it's also possible to get it shipped (done that, too). I suspect that's how they get it (order it from a distributor in Chicago).
I believe the neon green relish is Chicago-style relish. Since Fab uses Vienna beef products they may also be using Vienna brand relish.
There's some info about it on this web page: http://www.hotdogchicagostyle.com/testlab.php
"The Vienna branded relish is a
product of CHIPICO (Chicago Pickle
Company). As expected, it is bright
neon green and is a perfect compliment
to your Chicago Dog."
(The page also mentions some other relishes which they prefer to the Vienna relish.)
I'm not sure where you can get it in LA, but It's available online at: