If you’re hitting dead ends on Shopee and Lazada for 350-400 mg options, it might be a good shout to hit up some local health food stores or bigger pharmacies like Guardian or Watsons. They often stock a wider range of supplements that might not be as visible online.

Regarding brands, I've heard good things about Now Foods and Doctor's Best. They both offer magnesium glycinate around the 200 mg per tablet, so you'd need to take two to hit your target. These brands are generally well-regarded for their quality and effectiveness.