I know of a situation in Cuba where the literature for the dive operator specifically indicated that the boats had oxygen but they didn't. I think this forum is going to be the best place to check on these types of questions.
I would be totally impractical to take oxygen with you. You would have to acquire it locally which I suspect would be next to impossible.
Even if you have oxygen locally I suspect that it would only last about an hour. Unless there is way to get to the chamber quickly (air ambulance), I suspect that you would only have oxygen available for part of the trip.
Unfortunately, this is one of the risks of diving in remote locations.
I used to have a rule that I wouldn't dive with any operator who didn't have oxygen, a head, a radio and who didn't keep someone on the boat when we were diving. In some locations trying to find operators who can provide that level of service is impossible. For example, when I dive in Saba some operators don't have any of the above. However, the dives are rarely more than 10 minutes from the chamber, you can easily swim to shore and I guess I could pee in my suit if I had to, so I have been prepared to run the risks.
Everyone has to decide what they are comfortable with and what they are not comfortable with. However, I wouldn't want to be caught far from a chamber without oxygen.