Personally, not a fan of custom stands. Plain bevelled acrylic blocks and u-tables of varying sizes are most useful, I find. The majority of our purchases, for display, are made at Krantz, the oldest operating geological warehouse. They've a wealth of material available. Well worth a visit to their website, even if just to get an idea of options.

Agree with Bob, one ends up looking at the stand more than the specimen. :)

Oh, seemed I missed the point a little. For those specimens not catered for, I find local wood-workers of much aid. Practical folk, who try to accommodate.