Sprite distributor

I've an inventory system, 500+ unique sprites.
What's a good way to fetch a sprites?

Currently I just cycle through a bunch of spritesheets and throw all their sprites in a dictionary like this

Code (CSharp):

1.         string root = "UI/Inventory/Items/";
2.  
3.         for ( int i = 0; i < 17; i++ )
4.         {
5.             Sprite[] s = Resources.LoadAll<Sprite>( root + i.ToString() );
6.  
7.             for ( int j = 0; j < s.Length; j++ )
8.             {
9.                 sprites.Add( i + ", " + j, s[j] );
10.             }
11.         }

And get the information like this

Code (CSharp):

1. internal Sprite Get( int subcategory, int  categoryIndex  )
2.     {
3.         try
4.         {
5.             Debug.Log( string.Format( "Fetching {0}[{1}]", subcategory, v ) );
6.             return sprites[subcategory + ", " +categoryIndex ];
7.         }
8.         catch ( Exception )
9.         {
10.             Debug.LogError( string.Format( InventoryItemRoot + "{0}[{1}] not found.", subcategory, categoryIndex ) );
11.             throw;
12.         }
13.     }

But it feels pretty impractical having 500 odd sprites loaded all the time.

 

instead of pre loading all use only resources load on the sprite you want to get.