I've heard white art sand you get from craft shops does the trick and dries clear'ish too.
Although some clears (especially the oil based poly's can yellow with exposure to UV, so it'd pay for a DIY'r to research that). Minwax water based polycrylic is good on my skaters and doesn't yellow, it might be ok for the job. Never tried it on an sb or sup before though.
The Nalu wasn't cheap so I just went with the tried and true.