Please show me the keyboard layout that has keys for ⁺, ř and ₚ.
(Unless you're being pedantic because I wrote "keyboard" rather than "keyboard layout", or ignored the qualifying "pretty much". In either of those cases you're unwilling to communicate cooperatively and I can't help you.)
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.
(Unless you're being pedantic because I wrote "keyboard" rather than "keyboard layout", or ignored the qualifying "pretty much". In either of those cases you're unwilling to communicate cooperatively and I can't help you.)