This is such a delightfully delicate tasting vegetable it's a pity it isn't more widely available. I have occasionally bought it in Sainsbury or Waitrose, or if you're lucky enough to have a local farm shop or local farmers market you may well find it there. As mcfluff advises, asian and other ethnic foodstores are also worth checking. But it's not easy to track down as few people seem to know how to cook it, although it's also delicious raw in salads. If you've got a spare patch in your garden it's not too late to buy a packet of seeds from a garden centre and sow some.