I wasn’t thinking about the 2 digit and one digit cases when I first posted. For the one digit cases, I have an image for every letter. It is a bit arbitrary about why they are coded as one digit, but I know them.
For 2 digits, I used the letter H which is not in my phonetic code for numbers to be a filler letter that makes a 2 digit number instead of 3. This made the 100 images for 2 digit numbers. My original 2 digit system phonetically fit into other parts of the list. I hope that helps.
Here is another link that may help. I don’t know enough about Spanish to give personal direction about choosing your phonetics. I do think the Idea in the link below has potential though.