Don't forget to have the Dwarven traveling merchant cart near the end of the campaign.
"RUNESTONES! GET YOUR RUNESTONES! KEYSTONES! FLAGSTONES!" and his cart is filled with cheap, imitation runestones exactly like the ones the party is looking for.
<player> BUT... these runes... they.... they....
<Dwarf> Not bad, eh. My boy took a fall last spring, and his arm has this twitch. So I gave him a paintbrush and voila, instant runestones!