Sometimes a match is marked as a "Friendly", which means its country is NULL, i.e. BetFair does not specify it. In that case it won't be found in any country, even if both teams originate from that country.
So yes, you need to look Internationally then.
How to check whether BetFair marks the event's country as NULL:
Add any market from that event to "My Markets". Press on the "i" button in the top-left corner of the market info panel, then look at the "Venue" field. See an example attached.