As others have said, those modes are non-standard. What hasn't been mentioned is that not all IRCds that support "owners" and "admins" agree on what they are capable of and what modes define them, making it difficult for mIRC to add those events and have them work as expected on each network. In fact mIRC does support an on owner
event already (undocumented), but I'm pretty sure it doesn't work with a lot of servers which have an owner status because of those varying definitions.
If you're happy to have it scripted but just can't get the rawmode handling sorted, there's ready-made code to handle it already available
Personally I'd rather see a built-in identifier for rawmode to make it easier to connect each mode with its argument, rather than having additional built-in events that might not work as expected on all servers. That way people could write a script that works for the servers they use with very little effort.