It's so unconveniant that searching some classic model from all internet.
QIDISlicer provide one function that can add some classic model to project really conveniant.
¶ What's the function?
Right-click some blankt space in the plate,you will find that a context menu has poped up,than you can move cursor to add shape tab,click the gallery tab just like below.
In the shape gallery poped up following,
We can select one classic we need,than the model will appear in the plate.