How do you get monster fluid in monster hunter tri

In shop you can buy it for 5000z which it is pretty expensive when you are a beginner.
You can also get them free by trying to kill Vespoids (those annoying mosquitos) to carve their Monster fluids.

It is often that Vespoids ends up 'breaking' their whole body which you cannot carve them. But it is not always so. If the Vespoid did not break its body parts then you can carve it for their items.

I do say that those Vespoids won't break for like 20% chance. But you can also throw a Poison Bomb at them to let them instantly die without breaking their body parts for 100%.
You can also use a weaker weapon (Sword and Shield, for example) with a poison element. Bows with poison coating also work.

While the above is true, the BEST place to get it is from Giggi and Gigginox.