score:3
I do like to push them - once again, if you're really stuck and don't know where to look, consider Flightfox. I'm not affiliated, although I do compete on there as one of their 'experts'. Basically they have a bunch of 'experts' that compete to find you the best price. With what may work best as an open-jawed flight or a double-return (Japan->Mexico return, Mexico->Venezuela return) will be investigated by people on there.
It's not a free service, but if you do want to use it, check out my profile on here for a discount link.
Alternatively sites like kayak and skyscanner are a good start if you want to do all the grunt work yourself.