I was having the same issue as you just use this drag the vrca file into asset ripper.exe then wait for it to say finished go into ripped and then exported projects https://github.com/AssetRipper/AssetRipper after you see all the files drag and drop them into your unity project you don't have to drag the scripts file into their unless you want to if you have issues with the avatar descriptor reimport your sdk
Here's a website to for some shape keys. there's many places out there to look but I hope this one is helpful.
https://learnmmd.com/Make-Your-First-Model-Using-Blender-by-Mae-Blythe/Make-a-Model-Part-21/index.html
Download Cats plugin and install it to blender.
Here's a vid on that : https://youtu.be/UNSatI6zycU
After you follow the tut on installing it, you just import the file as you do to fbx files. Then just hit fix on the cats plugin when you have the box open and it should fix up the pmx file then after that export it to fbx
You likely cannot find another website with the same avatar ripping functions. The best you can do is to find the original assets used to build the avatar, or find a similar model on ripperstore.