As I know that is the only way to acquire it
Just repeat that quest several time
Or do it with your friend to make it more quick

Go to any area that has a Giggi egg sac I find it much easier to collect Monster Fluid from them than getting it from those Mosquito things.

Another option is to keep doing the same quest, but take poison smoke bombs and use those to kill the bnahabras. It's an instant kill for the bnahabra which will make the body stay intact when it dies. Monster fluid can be carved from the carcas.

I found out from my brother that you can aquire monster fluids from bnabahra, altaroth and giggi.
Note : my brother said,"I got monster fluid from the altaroth and giggi @ the gathering quest"

Do quest at tundra beat gigi carve it + quest cart order your felyene to go to area that many bhanbara

Giggi,bnahabra, or altaroth smoke bomb them and wait for them to die, and carve but sometimes its not monster fluid ex. carves of altaroth -altaroth stomach or monster fluid so its rare or just beat tons of giggis at the tundra.