Actually, “available” is a poor translation of what the Indonesian sentence is saying. “Take every opportunity there is” is much better. Not all opportunities that exist are available, and the Indonesian sentence doesn't limit it to ones that are.
You make an implication outside the context of the given sentence, which you should not. Moreover, /every/ is /setiap/. I haven't tried with the word 'exists', though.
This translation is correct but not very natural.
"Take every available opportunity!"
"Take every opportunity you can!"