The antonyms for the word "most under-the-counter" can be "available openly" or "aboveboard." If something is under-the-counter, it means that it is sold secretly or illegally, without any official authorization. Therefore, the opposite of that would be something that is sold openly, legally, and transparently. For instance, prescription drugs are available over the counter, which means that they can be obtained legally without a doctor's prescription. Similarly, some products are mostly above board, including groceries, books, and electronics. These products are sold openly and legally, and there is no need to hide them from law enforcement agencies. Therefore, it's important to purchase goods and services from legitimate sources to avoid any legal troubles.