Look in the Maya help under "Use image sequence" option found in the file and movie material nodes. When you check "Use image sequence" Maya assigns an expression, but for more control, delete the expression connection and then assign key frames. For example, set a keyframe of 1 in the "Use image sequence" box at frame 1 of your time line, and then srub to frame 30 of your time line and set another keyframe of 30 in the "Use image sequence". Then open your graph editor, and select the file node curve "Frame extension", and click on the menu item "Curves" , "Post infinity" and choose "Cycle" or Ossilate.