Try Pella Window & Door if you have one in your area. Go to pella.com to find the locations.
You can have one made in any size, the most economical, (with just a 10" height), would probably be one that is inoperable, (fixed). Ask for a clad frame, they're all custom made to the size you require.
In a bathroom keep in mind that you will probably want tempered glass for safety. That way if it breaks it falls into harmless glass 'pebbles', that are not dangerous.