Call around to all of your sand, gravel, and industrial 'substrate' companies in your area. You'd be surprised at some of the variety you might come across.
A new LFS in my area makes special trips to Portland, OR. There is a company their that produces tons of varieties of natural decorative sands and substrates, for gardening and crafts. Costs about $4/50lbs, and it is the only place I have located a 'FINE SMOOTH AGATE GRAVEL' (not sand) that is completely natural and neutral. It is large enough to not compact or ruin a filter, but small and smooth enough to be completely ray/geo safe and still have that very nice natural sand look. I can take pics if you want.
Also look for the 100% quartz pool filter sand that is the 'larger grain'.. Good luck jer