The source is just lowly Wikipedia for MkIV production alone. MkIII tanks and SPG chassis, even if MkIV based, would be separate. German tank and SPG production is pegged at 67,000, or about 2/3 American production. This jibes with other sources I have seen.
The figure illustrates the problem for Germany, since it does not even include British and Russian production. American production of other mechanized equipment, such as trucks, further overshadowed Germany.
“...lowly Wikipedia...”
Haha! Wiki gets it right sometimes...