All of these methods are only practical if there are really very few flights between the two countries. So if you want a list of all flight numbers between the USA and Canada, you'll have to come up with something yourself :)
On the flight search engine kiwi.com, you can enter entire countries as both origin and destination, and you can specifically look ...
In this case, it's easy since Paraguay is small and apparently has only one airport that serves international commercial flights. https://en.wikipedia.org/wiki/List_of_airports_in_Paraguay
The easiest way would be to look at the map in flightconnections.com and click on the airports that show up. In Paraguay that's only for and only Asuncion (ASU) is the ...
The Flightradar app allows you to search by route.
Searching for the route VVI (Bolivia Viru Viru International Airport) to ASU (Paraguay Silvio Pettirossi International Airport) brings up three flight numbers.
Some of these flights go to MVD airport but there is a direct flight every day.
Skyscanner is another that provides email alerts for price changes, I also use it to find the cheapest flights for any given route as it compares all available flight combinations for you, and if you are flexible about your dates you can view the search in month mode see the price for that route every single day, sometimes you can save significant amount by ...
Flight prices often go down and up within short periods of time - I have seen specials offered for less than an hour. It could well be that the Google Flights search result is updated only once per day (or every 8 or every 4 hours), so the amount shown is simply outdated - it was available a while ago, but you 'missed it'.
Unfortunately, there are also many ...
Like the other answers I'll share my tools that I use, the most common ones are: (with no affiliation to them) are skyscanner and greatescape I feel like they are both underappreciated for the amount of things they let you do.
You are able to put in the airport of your choice and then get a list or map view of all the destinations you're able to reach from ...
I found a very similar tool, but with advanced functionality. You may see baggage allowance, aircraft model with the tail number on the route and airport schedule with arrival and departures. The synergy of the flight radar and direct flights mapping https://flightsmap.org