Hi vitaminmigiraine,
I'm sorry you are having a difficult time finding a preventive regime that helps. Persistent aura is a problem for a small number of people with migraine and you're correct - there is not a lot of data on treating this. There is some anecdotal evidence that acetazolamide, brand name Diamox (which is similar to methazolamide) and valproic acid (Depacon) have helped some with persistent aura. This page has good information on this type of aura; http://www.migraine-aura.com/content/e25968/e26078/e26305/index_en.html.
Here is a research poster with interesting information on this topic; https://www.bcm.edu/departments/neurology/pdf/poster_other_VisualAura.pdf.
I take methazolamide for idiopathic intracranial hypertension (https://migraine.com/blog/migraine-comorbidities-idiopathic-intracranial-hypertension/ and find it helpful. But this is different from persistent aura.
Something to keep in mind is it can take up to three months before we see a reduction in our migraine symptoms. Also as our body adjusts to the new medication potential side effects may lessen.
Please keep us posted on how you are feeling,
Nancy