yea, do! oxide has the highest amount of elemental magnesium but it is the least soluble and you can't absorb it properly when it's zooming through that fast. try for the glycinate form. it will do you much more good.
my current brand is kirkman, but i don't know where it came from exactly because my mum picked it up somewhere.
the zinc sounds great. well done on the copper component.
retests in november sound great. at 10,000IU/d, don't be surprised if you end up testing high once you get the right mix of cal mag and zinc.
the d3 level needs to stay under 250nmol/L so you may want to think about dropping to 5,000IU/d now that you've added a zinc supplement too.
and lastly, i usually get supplements at places like 'nutrition house', or any organic grocery with a wide variety of nutritional supplements.
hope that helps!