What scale? Always state the scale.
The US naval mount for the 25mm chain gun is designated the MK38 Mod _. The army designation is M242. You may want to change the search parameters to 'MK38 25mm chain gun'. Not to be confused with the MK38 5-inch gun of WW2 vintage
Veteran Models offers MK38 Chain Guns in 1:350 scale. Try Shapeways for other-scale offerings