Cindy,
I can only assume you tried the very three Mexican grocery stores that do not carry Jamiaca concentrate
However, I think you need to keep trying. I would try little village, but there are probably some stores closer. I know also the juice drink (actually a tisane) and the dried flowers are sold at Maxwell market. You might inquire from one of the vendors where they get the concentrate or if they make it fresh.
I believe I purchased concentrate once at Jimmenez on Western near Fullerton, but I assume many more have it.
pd
Unchain your lunch money!