I recently discovered a phenomenal tool for listing the SPNs. You can find the VBScript on Microsoft's website below:
Using this tool, you can locate any accounts with Application SPNs as follows (you can name the VBScript whatever you like):
C:\cscript queryspn.vbs App123*
Running the script above will list out all the accounts (with all their SPNs ) with SPNs that begin with "App123"