power brake booster

Hi, I'm new to the forum. I just bought a 1977 Ltd 2, 302 w/C4. 97k miles. I'm in the process of fixing it to be my new daily driver. I had to send my brake booster in to be rebuilt, due to the fact that I couldn't find any available. rod code "FF10" does anyone know where to find one? I assume this is a common problem?! Does anyone know of an aftermarket solution? Thanks in advance.