Lombards is a great shop for any party supplies. They've got lots of helium balloons and anything you need for a party (except food). The staff are really friendly and aren't too pushy for you to buy anything. The great bonus is there's a shop called dance art in the back of the shop which is great to either hire or buy costumes as well as buy dance-wear. The dance-wear at this shop has big brands (Bloch,energetics etc) and they are always on sale or at a bargain price!!
Great shop, it's just a shame the products are a little pricey, wonderful service from staff. Always polite and willing to lend a hand.