You can try with the build-in signature for FTP brute force:
IPS engine marks traffic based on packet content instead of port mapping, unless a specific port is specified in the signature (it is not in this one) therefore if traffic is ftp it should match regardless of the port number.
Now since you ask for FTPS, you will have to configure your ssl inspection profile accordingly and since it will be in "protect server mode" if you are protecting a server, you can only do this part in CLI, for example:
config firewall ssl-ssh-profile
set ports 2222
set status deep-inspection
set server-cert-mode replace
set server-cert "test_cert"