I don't know any official figures for numbers of Mk IV made.
Approval for the Mk IV was dated 6 September 1918, but production would only have begun once the relevant contractors had received necessary instructions and the running Mk III contracts had come to an end. As of 2 December 1918 it was recorded by the Controller Munitions Design that there was "NO stock of Mk IV" and "NO stock of Mk IV M". This suggests that other than small numbers made for trial use, full scale production and delivery had not commenced.
From December 1918 to May 1919 around 300,000 empty No.34 were delivered as contracts were terminated, but it is very unlikely that many of those were Mk IV. Within hours of the Armistice happening, instructions had gone out to cease production of many natures of munitions, and any new designs not yet being produced would have been put on hold.
Tom.