There is more than one solution to this.
The easiest, is to create a behaviour which will make the sprite face the camera always, and call MakePixelPerfect on it every frame.
The second is to put your sprites in the tk2dCamera scene, get the position from the perspectivecamera, use camera.WorldToScreenPoint to get a screen point, and then use tk2dCamera.ScreenToWorldPoint to transfer the coordinate to the tk2dCamera. You will need to adjust the z coordinate, but now the sprite can just be in the tk2dCamera, just use this logic to reposition every frame.
If you want to instantiate sprites, create a prefab and instantiate them.