In most big Sainbury's you can get dairy free ice cream. They do their own range, 'Free From', but I think its kinda rubbish. They also carry a brand called Swedish Glace, much better. Its also available in Holland and Barrett. If you can get near a good quality, usually independent, health food shop there is a range of ice cream called Tofutti. They are the Hagaan Daz of the dairy free ice cream world.
Provamel, stocked in most supermarkets, H&B and healthfood shops, do, I think that nicest soya milks. Following that So Good do a great chocolate soya milk. Whatever you do don't get Asda's soya milk it is truly gross.
Always get the sweetened form of soya milk, the unsweetened stuff is usually an acquired taste.
Provamel also do a range of chocolate with soya milk if your DS hates plain chocolate, though it is a bit cardboard tasting.
I was a vegan for 7 years and still find dairy too hard to tolerate.
As for a directory, I can't think of any off hand but will do some digging. I'll let you know of any more dairy free if I think of it!
HTH