The US Army formed a similar ad-hoc formation in the Philippines with the 65th Cavalry and the tank battalions, I believe. Would such units be formed pre-war as regular independent formations? The Philippines looks like a possible candidate for such a unit.The Germans created such units in WW2, lots of them in fact.
Kampfgruppes.
You could easily make the Kampfgruppe equivalent of an ACR, considering that the Kampfgruppe was often a ad-hoc unit and didn't really have a fixed size.
Sdkfz 234s, as they have 5cm AT guns, 7.5cm support or 7.5cm AT guns.
Probably late model Panzer Is and IIs, the type with overlapped suspension and heavy armor.
Krad Schutze (motorcycle infantry) is a must, along some motorized infantry in Blitz trucks.
Probably some Sdkfz 250/251 based AA or artillery as well, to round it out.
Let's say a German commander like the Panzergraf was assigned to take an important objective that was far away but of viable importance to the campaign.
He would look at what he had available and make a Kampfgruppe out of the above elements I listed.
And that would basically be what the Western Allies would call a ACR, but to the Germans it would be a Kampfgruppe.
The odd independent armored/panzer/tank or mechanized brigades were formed. Are they that different from an ACR? Did ACR-type formations already exist or were forming in the 1930s?