Buy another reed (identical to the one you have) and you will double your ends per inch. For example two 12.5dpi (50/10) reeds will give you an amazing 25 ends per inch (100/10)!
Please note this works only for the Rigid Heddle loom and reeds. It is not compatible for the Knitter's loom and reeds. Please make sure you are ordering the correct kit of your loom.