In addition to the points people have already mentioned, it is possible that when you're doing your groceries, that your subconscious notices items which you aren't looking for that day. You tune them out because your mind is busy with other matters, but the idea of a lobster or a goose or whatever gets into your thoughts, gives you a craving which you then discuss, but the lobster or goose were on the shelves before the conversation & before the craving.

The same can happen with things like advertisements promoting a special deal this weekend, or whatever. We don't have to be paying attention or have any conscious awareness of the ad to get the idea "mmm, lobster", "oooh, goose" in the days following.

On top of that, the supermarkets have a sense of what situations make large numbers of customers interested in specific categories of product. So, the start of autumn can make people begin to think about ordering a big bird for for Christmas, summery weather can make people want shellfish to grill outdoors, etc.. The most obvious examples would be special offers on all of the items that are popular for BBQ when there's a hot dry spell, or stocking Christmas pudding & mince pies in the run up to Christmas. Yes, one can get these things at other times of year, but they're not promoted and are often tucked away, or you have to ask at the counter. In this sense, your cravings and thoughts about produce may just accord with that of others in your community, and the supermarkets' stocking is just a reflection of those trends.