In addition to the shadow, top clamps from a VTX1300 work as well. You only need the top part. They work with the Valk lower risers.
Use the Hondaline chrome riser caps from an 1100 Shadow.
Did this with several of mine.
Alternatively, I have an aftermarket set of Magna two-piece riser clamps (square profile) which may work for your application. They're not chromed like the Hondaline accessory, though - polished raw aluminum finish.