There's one in the first Mason-DixonKnitting book. It's called Mason-Dixon AFter-Dark Robe. It's sized for a woman, but not particularly feminim-looking (no lacy bits).
Another in this book: Home Knits: Luxurious Handknits for Every Room of the House
Maybe find a loose cardigan sweater, make it longer and call it a robe.
For the books - try your local library.