I've been looking through relic castle and route 4 in Pokemon Black 2 and yet I couldn't find Rock Tomb and Dig anywhere in one of those poke balls lying on the ground? Is this a fault or do I have to look in
Neither of these TMs are hidden items, so it is interesting that you haven't found them.
On Route 4, Dig (TM28) is located on a hill east of Policeman Neagle. In Relic Castle, Rock Tomb (TM39) is on floor B1F, near Psychic Dua.
If it makes it easier, I recommend checking Bulbapedia for more in-depth guides.