pathfinder 1e – Can I use a Runestone of Power to cast a spell I normally cant?

Yes, and no.

You can certainly use a Runestone to cast a spell that you have gained via a Page of Spell Knowledge.

Page of Spell Knowledge says

If the bearer is a spontaneous spellcaster and has that spell on her class spell list, she may use her spell slots to cast that spell as if it were one of her spells known.

and Runestone of Power says

Once per day, a spontaneous caster can draw upon a runestone of power to cast a spell […] and expends that runestone’s power for the day rather than one of the spellcaster’s actual spell slots for the day.

So we can treat the spell on the page as being on the users list of spells know, and can cast it with one of our spell slots.

We can then use a Runestone to expend its power instead of using one of our spell slots, allowing us to cast the spell via the runestone.

We cannot, however, use a Runestone to cast a spell of a higher level than we have slots for. From the items description, it allows the use of the Runestones power instead of one of the spellcasters spell slots.Since level 9 sorcerers only have up to level 4 spell slots, then there is nothing for the Runestone to be used in place of.