Desk research against primary sources, with the issuing authority linked where a page states an official fee, rule or deadline.
The same active ingredient can sit in either category depending on the formulation and the stated purpose, which is why some antihistamines are freely available for allergies but restricted when marketed or dosed as a sleep aid — the ingredient is not what decides the classification, the product and its intended use are. This makes a home-country label an unreliable guide, since a medicine sold without restriction there under one formulation may be sold under a different, restricted one here.
For anything that turns out to need a prescription, the pharmacist can usually tell you which nearby clinic can issue one quickly, which is often a faster route than trying to work out in advance where to go. Asking the pharmacist directly before assuming an item is unavailable is generally worth doing anyway, since the classification is not always intuitive, and a quick conversation at the counter is faster than discovering the restriction only once you are ready to pay.