An added note: the best way to get "relearning items" is in FR/LG. Get tons of money (VS Seeker at Resort Gorgeous), buy many, many Ultra Balls, then hop over to Mount Moon, where you can find 100% Paras in the tunnels. Catch each one you see (they'll generally stay in an Ultra Ball, even without being weakened). When you've had enough, use an Escape Rope and remove all TinyMushrooms via Move Items, then release each Paras. This takes much less time than searching in the Safari Zone for Parasect.
If you have Emerald, you can also clone Heart Scales using the now-popular cloning trick.
Once you've found all the hidden scales in Ruby or Sapphire, however, there's really no easy way to get more since the only way is to find wild Luvdiscs with a Super Rod.