there are aftermarket and performanced full amp load ammeters in the market.

but why don't get an used replacement amm gauge for the cluster like it was and aftermarket underdash voltmeter ?

trust me, you don't need more than 40 amps gauge in dash... and if you do, something is wrongly hooked up. A discharged batt will never get more than 40 amps to be recharged. Chemicals are not that fast.

And if it does, something else is wrong, aside a fully discharged batt never must be charged back on car... not at least taking care of some other stuff