> Search for compose key sequences.

I don't need to do that because I actively use them myself and have a custom ~/.XCompose. Also, please try communicating less condescendingly.

There is no default compose sequence for ₚ that I can find, at least in my Debian installation.

So, again, please point me at the layout that can output these characters.

And even with that: if you don't think Compose sequences, possibly even custom, are covered by "pretty much impossible", I must seriously question your perception & bias of how common (or not) things are.