Do you remember the plates we found in Sinnoh I found out a way to get them to both soul silver and heart gold. After you beat the Champion you will beable to use the SS Aqua. After the first time you use it, you will be able to use again on these days: Wednesdays and Sundays from Vermilion
and Mondays and Friidays form Olivine
On these days if you talk to the Captain he ll tell you that he found something in Sinnoh region the other day and he ll give you a plate.
Hope this helped!