As of last Friday, autumn is officially upon us. In Keats's words, it's the season of mists and mellow fruitfulness – with the latter being of far more interest to foodies. Now's the time of year for mushrooms, mulled wine, pears and pumpkins. September also marks the start of Girl Scout Cookie season in the States.

Girl Scout Cookies (pictured) are an American institution. Packed in brightly coloured boxes, they are sold across the country to raise funds and to teach girls entrepreneurial skills (the most successful sellers not only get a biscuit-pushing badge but win time at camp for their troops). Girl Scouts have been selling cookies since 1917, when their wares were homemade and the American scouting movement was only five years old. Now the biscuits are a multimillion-dollar business (last year, 198 million boxes were sold, earning more than $700m) and two huge bakeries hold the licences to make them.

GSCs contain no girl scouts but come in a variety of flavours, some (Thin Mints, Samoas and Shortbread) that have been scoffed across the States for decades, and others that have been added in recent years (Thank U Berry Munch, Dulce de Leche). Scouts sell them to friends, family and from stalls in supermarkets. But they can't do it online. One scout with a web-designer dad got in hot water recently after her internet cookies site was deemed unacceptable by the girl-scout council.

The average Brit probably isn't going to be that fussed that Larissa in Louisville can't use e-commerce to increase her sales, because they won't have eaten a Girl Scout Cookie. But having tasted the forbidden fruit (well, a box of Thin Mints brought back last year by my husband from a business trip), I have become obsessed with sourcing some. I'm not alone – even in the States, cookie-heads can only score their snacks at certain times of year (from September in some states, until April), and there are forums awash with tricks to making a stash last (buy in bulk and freeze carefully) and recipes to bake your own (goo.gl/AWclv). There's a roaring illicit trade on eBay, but the scary girl-scout council is so stern about buying from non-official sources (because the scouts in question don't receive the cash for camp-outs) that I feel too guilty to click the "buy now" button.

In my bid for biscuits, I contacted Girlguiding UK to see if it could come to Britain's aid. Alas, while Donna Holland, the Girlguiding's fundraising manager, tells me she thinks that the Girl Scout Cookie programme is "brilliant", on this side of the pond, Guides are encouraged to decide on their fundraising activities themselves. So if anyone is planning a September trip Stateside, please, please pick me up a couple of packs...