thrust bearing is the bearing in your gearbox that is relative to your acceleration. i had the same think with my old EG civic, replacing the whole gearbox was easier and cheaper than replacing the bearing, that being said, i did this before learning about a honda mechanic who can do it easier, but im not sure how easy or cheap holden gearboxes are to work with, but theres no "quick fix" for it, if you find a holden mechanic, id say replacing the bearing with cost around 300-600? i think they have to pull the gearbox out, pull it apart, and run a kit through it.
In may also be your main shaft bearing, the main shaft bearing will not make noise when on idle or stopped, but as you accelorate through each gear the noise will speed up as your revs speed up, the main shaft bearing will stop making noise if your driving and clutch in. (just checking that its the right bearing)