There appear to be a good selection of cable amplifiers. Here is a snapshot I grabbed, but haven't done any research and make no claims regarding any of these products.
The amplifier needs to be bi-directional if you are using it for an internet connection. Some of these at first glance look promising. Keep in mind that your incoming signal needs to be relatively good. An amplifier can't fix a poor signal level or noisy input signal, it will just amplify the noise with the signal, i.e. signal to noise ratio doesn't improve.