Many pain meds are available in costa rica, but not all of the ones that are available in the US. Many narcotic ones such as Temgesic, Demerol or morphine require a strictly-controlled "green" prescription from a Costa Rican doctor. Codeine preparations are available over the counter (such as codeine + APAP), and tramadol (known as Tramal) is available in many different forms (50mg capsules, 100mg 12-hour tablets, and injectible). Tramal is made by Grunenthal, the original discoverers of tramadol in 1962.

There may be others, and you'll also find that doctors are more likely to prescribe them for appropriate conditions than they are in the US.