Filter sand in Guatemala

I’m looking for filter sand suitable for slow sand filtration (effective size of about 0.25 mm and a U.C. of about 2.0). For our pilot project we hand sieved locally available black volcanic sand with some success but that method won’t work well for the second phase of the project, which will involve over 150 cubic feet of filter sand. The regular 20/40 swimming pool filter sand is available, but what we need is more like a 30/60 sand. The project is a couple hours out of Guatemala City. Any leads and advice is appreciated. Thanks.