If you have travelled to a country where there are almost no halāl restaurants, is it allowed to order vegan/vegetarian food, at the risk that there may be cross contamination with non-halāl food? What do you do in such a situation, assuming you are already there?

Do not eat in restaurants that serve pork and alcohol, because their utensils and oil are not kept apart, and food cooked on the same surface or with the same knife as pork is not allowed. Buy from shops instead that which you can cook or quickly prepare without risking something forbidden. Also, I highly recommend searching online because, almost certainly you will find Muslim sources.