That’s strange, not listing normal single speed pulleys.
They don’t list the Rohloff adapter either, just a note about contacting them for details. I know they sell them because that’s where I bought mine.
It’s worth contacting them. I tried to order some stuff once and one item showed as “not available in your country” for no reason. I emailed them and they sorted it out straight away.
Never heard of Bikeman before.
That’s another thing that puts me off belt drive.
Gates keep adding to the list of obscure low volume manufacturers offering a belt drive bike on their Facebook page, yet they go out of their way to make it difficult to buy replacement parts.