Anyways though, you should be able to make an FBX out of an already existing prefab from the VRCA you exported presumably. Though if it doesn't export to blender properly, aka has screwed up weight paints and blendshapes... Then chances are that the model has been ripped quite a few times and uploaded, winding up with a version that you have that has probably been ripped maybe a dozen or more times by this point. But if it's the first rip of a model then you'll be near guaranteed to have a fully functioning almost fbx for importing to blender.