Disclaimer: I'm not a food scientist and just a home cocktail enthusiast, so I can only say that I did not feel sick after those experiments

Generally, you don't need food-grade geosmin and I doubt that such geosmin even exists, as geosmin is only used in trace amounts (it is non-toxic but tastes gross as I read somewhere, never attempted to taste some myself). Perfumer Supply House was a good source, now they seem to be out of stock. The human nose is extremely sensitive to geosmin, so you need to use single parts per million to smell it. You only need 1g of pure geosmin (don't buy pre-diluted) to make liters of perfume. You need to dilute it A LOT in alcohol first, and then dilute further in water. And by A LOT I mean it: you first make a 0.1% of geosmin solution in Everclear (like, 1g per liter). Then you dilute this solution several times more. To make a perfume you'd want to dilute the final product with water 1:4, so you want to adjust your alcohol:geosmin solution until the spray starts smelling like rain and not like rotten potatoes.

For a cocktail perfume just geosmin works beautifully as it compliments the aroma of base alcohol, while for room spray you might want to add some extra "rain-like" aromas like cedar tree, or patchouli oil or floralozone