Sometimes you can find level 9 fly traps in Cuba. The best thing is to make sure you have people with you that can help you. You might also want to try the flytraps in Tortuga also.
If you want to play solo, what you can do is make some damage on the flytrap, go to jail, and then go back to that same flytrap. I remember one time it took me about 6 times of going to jail before I got that flytrap
