Rotax offers an external alternator (example: for 912ULS), but not a higher-current replacement for the integrated stator.
Edge Performance in Norway lists several options for stator upgrades or add-ons in their web store but I think you may find that some models have been discontinued. You can contact them directly or reach out to one of their dealers.
-----
When you do your load analysis, remember to consider the duty cycle of electrical loads. For example, the VHF radio specifications might show a peak current draw during transmit, but that's only valid for a tiny fraction of the time. The same applies for the transponder, just with a higher duty cycle. Ditto for strobes, and even landing lights if they flash or wig-wag. The only relatively constant loads in the plane will be the engine electronics (ignition, and if you have an iS engine, the ECU), the instrument panel and always-on lights.
-----
Edited to add lights to final sentence.