The Vic spares kit contains a selection of the standard CT bits. If you can find a shop which sells Vic spare parts (pens, tweezers and so on), there's a good chance they'll have the bits too. Ask for a rummage.The non-standard CT bits, such as the (extremely useful) 2mm and 2.5mm hex drivers are much harder to find in the high-street. For these you'll most likely need to put in an order directly with Victorinox. They cost me CHF2.50 each.Sadly Vic doesn't make a 3mm Hex driver at all.
My plan is to go down to the hardware store tomorrow and see if they have these things in 4mm sizes (no idea what they're called in English)