While we do not have an adapter per se that works specifically with their fitting -- and we don’t have one of their models here to confirm -- generally speaking a generic step adapter commonly available might work. Many of them are tapered with multiple steps and are cut-to-fit. Otherwise you could consider purchasing a Festool hose (27 mm recommended) and it will likely fit into the receiver of the Bosch unit, since that is a fairly common diameter for those instances. In this case a non-antistatic hose (452877) would do the trick. Again, we don’t have one here to confirm, so maybe another member can confirm this for fit.
You may ask why we would recommend a 27 mm hose. Basically, when sanding, a smaller diameter hose is more flexible and less cumbersome to work with. Also, the finer dusts of sanding don’t require the larger diameter hose that is generally used for clean-up tasks or extracting from tools and machines that produce larger dust chips (like planers, routers, etc). This is one of the reasons why the 27mm is a standard diameter that is supplied with our dust extractors. It works well for nearly every tool, and especially for sanders.