I had one made by a local luthier and fitted for my bass. I also bought the tools to install and remove it myself. I don't think any bass builder has a second sound post option, but I could be wrong. I think Jason at BC still offers a built-in double post system you can add to your order, but I wanted the option to install and remove one myself. Here are pics of my bass, the tools and second sound post. Again it's custom made for my bass so yours may end up looking different.