In my city, Neem oil is available in almost all garden centers, and garden departments in the big box stores. Look for it in the area where the (so called) organic products are displayed. Neem oil is derived from a tree, Azadirachta indica. Cold pressed neem oil, without additives, can be considered certified organic. Many companies add surfactants, stickers, emulsifiers and other ingredients to enhance the product's effectiveness, but 'may' cause it to lose its 'organic' status.

In my area I can't find pure neem oil anywhere but online, but I can find products made with it such as Safer Bio-Neem at some nurseries, but generally not big box stores.

Neem oil is a natural pesticide, but it doesn't work the way you are probably thinking.

It doesn't kill much, if anything, on contact. It is a toxin when ingested by insects (and harmless to people/pets). Once ingested the insect stops feeding and dies over the course of days.

Because of this it is considered 'soft on beneficials' as it's only the insects that eat sprayed plant material that experience it's toxicity.

In my own yard I have also noted a repellency effect. Plants I know have insect problems each year get sprayed before the pest arrives and often they won't bother the plants at all.

Neem oil also has a mild anti fungal side to it. It is not a product I would use to try and cure a plant with a fungal problem, but it is a product I use on plants prone to developing fungal problems and it seems to do a good job at either preventing the infection from taking hold or slowing it's onset.

It's one of those rare products that's actually effective and can be used with a clean conscience in terms of the environment and one's self, family and pets.