Sometimes you get a disk image that can’t be nicely mounted. However, you’d still like to retrieve any ssh/rsa keys. Found a nice article that will get you close to the answer: http://amandine.aupetit.info/291/ssl-private-key-file-recovery/
grep -i -a -B30 -A50 'BEGIN RSA PRIVATE KEY' /dev/sda2
The only things I changed were that 30 lines before, and 50 after is a little much. 5 before and 30 after should capture MOST keys. If you see a long/secure key, it may be up to 50 lines, but then you can just refine the grep for later.