you can buy culinary lavender at Weirs Lane Lavender & Apiary, near Dundas, Ontario. They have a lavender farm. Quality culinary lavender from a producer has been processed specially for safety and human consumption. Also the lavender contains buds that were collected before the lavender bloomed and contains no stems or leaves. There are many types of lavenders and some work well in dishes, some do not. Each type will provide a different type. Lavender of the English variety (Angustifolia) is more commonly used. Lavender of the French variety (Lavendin or intermedia) is trickier. There is a higher camphor content and so your dish can be easily ruined if not used correctly. Of the French variety, Provence is a good choice.
In terms of lavender used for sachets, etc. a reputable/ high quality lavender supplier does not die or alter the buds. You do not want to use them simply because the care in debudding the plants and storing the buds is not the same if the buds are not being used for culinary purposes. Also for sachets, the buds tend to be of the French variety and a type that is not recommended for cooking.