The movie "Captain America: The First Avenger" is widely available on various streaming platforms, including Amazon Prime Video, Google Play, iTunes, and Disney+. However, I couldn't find any information on whether a Tamil-dubbed version of the movie is officially available on Isaidub or other platforms.

Isaidub is a popular online platform that provides dubbed versions of movies and TV shows in various languages, including Tamil. The presence of "Isaidub" in the search query suggests that the user is looking for a Tamil-dubbed version of the first Captain America movie.

If you're interested in watching Captain America: The First Avenger, I recommend checking out official streaming platforms or purchasing the movie on DVD/Blu-ray. This way, you can enjoy the movie with high-quality audio and video, while also supporting the creators and rights holders.