Of course by the term "tanks for training" I didn't mean driver-training vehicle like this:
but a standard, fully combat-capable tanks that simply wouldn't be attached to combat units, but to school/training centre of armored troops.
Same applies for other types of armored vehicles, artillery, air defence systems, engineering, signals etc. etc. equipment.
There are no "standard rules" about how many pieces of any given type of equipment should be used by such schools nor how it should be organized, but there are some "usual ways".
Sometimes a school would have an integral unit (company, battalion, in some larger armies even regiment/brigade) with relevant types of equipment, sometimes a school would have a separate unit (that at least theoretically could be combat-capable on it's own) "working for it". As for the numbers of particular types of equipment in such schools it would depend on needs, training cycle etc. but generally these would tend to be a "tactically viable" amounts (platoon-sized, company-sized etc.). For an army like in Your AU, I'd say that schools of armor and of artillery would probably use battalion-sized training units (2-3 tank companies, company of IFV's and company of armored recce vehicles, for example).
And of course certain types of equipment, particularly those used in very small numbers, by small number of units, sometimes are not represented in their "combat form" in service schools, but simply one of the combat units "borrows" it's equipment for training (though most likely a school would have some training equipment for the type).