What if every location that could hold a sleek is evident just by
looking, assuming the character is a high-enough level mage (30?)

look in drawer

Inside this well crafted drawer is a ornate case that looks like it
might hold a wand.

look in case

The case is empty.

It's a little bit harder for mobs that carry wands, but it could
just be a tweak to their description so that sleek seeking magi could
see that this particular guy sometimes has one on him.

The result is that the locations where wands might be becomes much
more common knowledge, though where *your* wands are is still
something of a mystery. If this makes it too easy, you could increase
the number of possible places and include a bunch of spots that
could, but never do, hold wands.