No internal gun was ever fitted to a production Hawk 200. I don't even think anything ever made it onto the prototypes.
There's still (unless they've mucked about with the internals in the last ten years or so) a bunch of cutouts in various frames where the barrel etc for a single cannon could go (the design got downsized from two to one, IIRC) but the cost of fitting the internal gun (and complexity of AV mounts for all the avionics being shoehorned in around the gun) ended up settling the question in favour of the same 30mm centreline pod that the two-seaters use.