If you can't find the images when scraping, you can compose your own Mix image with MixMe from images you own.
Video Tutorial
You want to Add or Modify media for the selected ROM and recreate a Mix image
Here's how:
Drag by drag&drop or select the images corresponding to the different elements of the Mix then click on 'Save Compose → Mix'
ARRM will recompose the image by applying the previously selected template.
You want to Add or Modify media for the selected ROM and keep the already existing Mix image.
Here's how:
Drag and drop or select the images corresponding to the different Media elements of the ROM then of the Mix then click on 'Save images without Recompose'