Are you able to offset the main texture? Here's a sprite sheet animator I wrote that you can $$anonymous$$r apart if that helps... I know it scrolls through textures, though I haven't tried it with normal maps specifically. It's probably way more than what you're looking for, but maybe you can find what you need in there...

 var sheetRows : float;
 var sheetColumns : float;
 var duration : float;
 var curFrame : int = 1;
 var incrementX : float;
 var incrementY : float;
 var loop : boolean = true;
 var loopCount : int;
 var animate : boolean = true;
 var curRow : float = 1;
 var curCol : float = 1;
 var initialOffset : Vector2;
 private var totalFrames : int;
 private var animationStart : float;
 private var lastFrame : float;
 
 function Awake()
 {
 initialOffset = renderer.material.mainTextureOffset;
         
 //renderer.material.mainTextureOffset.y = 1 - (1 / sheetColumns);
 
 curFrame = 1;
 curRow = 1;
 curCol = 1;
 
 if (duration <= 0)
 {
 duration = totalFrames;
 }
 
 if ((sheetRows > 0) && (sheetColumns > 0))
 {
     incrementX = 1 / (sheetRows);
     incrementY = (1 / (sheetColumns)) * -1;
     totalFrames = sheetRows * sheetColumns;
     }
     
     else
     
     {
     print ("Remember to set sprite sheet's column and row count.");
     }
 }
 
 function Update()
 {
     if ((animate) && (Time.time >= lastFrame + (duration / totalFrames)))
     {
         advanceFrame();
     }
 }
 
 function advanceFrame()
 {
     lastFrame = Time.time;
     
     renderer.material.mainTextureOffset.x += incrementX;
     
     curCol += 1;
     curFrame += 1;
     
     if (curCol > sheetColumns)
     {
         curCol = 1;
         
         renderer.material.mainTextureOffset.x = 0;
         
         renderer.material.mainTextureOffset.y += incrementY;
         
         curRow += 1;
     }
     
     if (curFrame > totalFrames)
     {
         ResetOffset();
     }
 }
 
 function ResetOffset()
 {
 
         renderer.material.mainTextureOffset = initialOffset;
         
         curRow = 1;
         curCol = 1;
         curFrame = 1;
 }
 
 function playAnimation()
 {
     animationStart = Time.time;
     
     animate = true;
 }
 
 function pauseAnimation()
 {
     animate = false;
 }
 
 function animationStop()
 {
     animate = false;
 
     renderer.material.mainTextureOffset = initialOffset;
     
     curFrame = 1;
 }