Answer: Your idea sounds charming. Since oats are a type of grass, and grass thrives in full sunshine, you should expect your arrangement to be only temporary if kept indoors.
I can't find a source of oats for you, but I'll bet you could find seeds in a health food store where other seeds for sprouts are kept. The vermiculite is a lightweight material often used as an ingredient in homemade potting soil. You can purchase small bags of vermiculite in the garden section of most well stocked stores. Fill a planting container with vermiculite, sprinkle seeds on top, and water well. The seeds should germinate within a week. Provide bright light and be sure to water once each day, because the vermiculite will serve as an anchor for the roots, but it won't hold enough water to sustain the grass for very long.
Good luck with your project!
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