After an extensive search throughout the city, I found one hotel having wifi cards! Another hotel had some that were three times as expensive and only worked in their hotel. I don't have enough cash left to risk that price. Even the wifi bureaucracy, Etecsa, did not have any cards. I'm guessing that the hotels have some special arrangement so that their foreign visitors don't get disappointed.
I'm somewhat seriously concerned about getting out of Cuba. I expect it at least to cost mucho dinero, and possibly be quite difficult. Still, I think I can make it.
I can't say that this is completely unexpected. I thought beforehand that getting among any Caribbean islands would be difficult, especially Cuba. I did as much planning as I could, given the limited time in which I knew I would go. I'm going to look for a new plane ticket, or alter my previous one, or see about a boat, or any other means.
You can't wait for the perfect opportunity.
Things happen anyways. Just go ahead.
Don't expect things to be easy. Most (or at least many) things worth doing are hard.
Often better to leave some off.
Generally better to give than receive.
Cuba is annoying to get anything done.