They seem to appear in our shops every year round about March or April, ready for summer holidays. (Anyone trying to buy them in November is doomed to failure.) My problem is that I wear them a LOT, including on long walks, so the fabric between the legs tends to wear through. The very cheap ones I bought last spring - a supermarket's own brand - have actually lasted a LOT better than the slightly more expensive ones I bought from elsewhere, which wore into holes within months.