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It seem that there is but the only way to fly might be a chartered flight. Air Panama which supposedly services the airport doesn't seem to have any scheduled flights to or from Santiago de Veraguas.
The only thing I was able to find are charter planes that are able to go to the airport. Which seems to be confirmed by a Panama guide book, which states that you can only charter a plane to fly into the Ruben Cantu Airport, the book also gives you some other options of getting to and from Santiago de Veraguas. So your best bet would be to take a bus or rent a car and go to Panama City and then take a flight to Bocas del Toro.
Upvote:1
There are flights from David and Panama City to Bocas which I have both taken. I suspect the one in David is closer. You would have to bridge the gap by land. Bus is probably the cheapest option.