All you have to do to refill heavy at the pleasure garden is take out the orange bar dudes. That's it. I refill my heavy 3/4 to full prior to every run. That's the entire reason for that pre-fight. The problem is, if you do not do any damage to them (or enough damage) they might not drop heavy for you. No member of the fire teams that I've been a part of has had an issue with heavy at that encounter.