We make new splined adapter on a regular basis. It seems as though no one wants an adapter you have on the shelf, they want one that is custom to their application. We will make you one piece or thousands of pieces. If you have to adapt a splined shaft to a different splined shaft, or a keyed shaft to a splined shaft, or a splined shaft to a larger splined shaft, we can help. Contact our Engineering Department and they will work you up a drawing and quote for your coupling needs.
Below are a couple Splined Adapter videos
Splined Adapters and Splined Shafts 
