The American and Canadian Association used to organize a concert and fireworks, but they shut their doors about 4 years ago, and as far as I know, no one has stepped in to replace them. It's fairly expensive to organize fireworks, and you are even required to have firefighters on hand if you want to be formal and legal.
But, a couple American friends are organizing a dinner at a restaurant in Miraflores for the US community here which will be held on Saturday (not quite the 4th, but oh well). Send me a PM if you are interested, along with your email, and I will put you in touch with them. There is only space for 35 people, and they are already halfway there, so first come, first serve, and subject to confirmation.