If you're having trouble finding certain parts in Studio, first refer to the following help pages: 

Finding parts

Filtering parts

If there are still parts that you cannot locate in Studio, here is a help article about part numbers:

Part numbers

Palette filters

If you can’t find a part, check that you are looking in the Main palette, that you aren’t filtering the parts in the palette by color or by decoration.

What's next?

Then, it means Studio doesn’t officialy have this part yet :( You can check in the community’s part repository if the part is in preparation. You may also check on LDraw’s part tracker if a 3D model is availailble, so you can import it with PartDesigner. Finally, you can ask on the forum for the part to be added.