Bromine is unusually concentrated in the Dead Sea, representing 0.4% instead of 0.0065% in the oceans:

https://en.wikipedia.org/wiki/Bromine#Occurrence_and_product...

The largest producer outside the Dead Sea is China by far, and the only other significant producer is Japan (!) which produces a paltry ~10% of worldwide output. It's possible to produce bromine from other places but you'd basically be starting from zero on the infrastructure involved. The short-term risks are real.

https://www.reportlinker.com/dataset/6b01d1a976f7ec9db71e35b...

However, it may be hard for Iran to disrupt bromine production. They may also not think about it.

EDIT: According to other links in this thread the US produces a significant but undisclosed (?!) quantity of bromine, practically all of which is consumed domestically. So it was probably missing from my data. Not great for other bromine users.