Wishing... I don't get it.

[Shadowcat]

You can wish for just about any item in the game, unless it is a unique item which already exists somewhere in the sector.

If you know for certain that you spelled it correctly and you still didn't get it, that tells you (1) that the item you asked for is unique, and (2) it's already out there somewhere.

IIRC Fomax will also say "I have THE (item name)" rather than "I have AN (item name)" if you successfully ask for a unique item, so pay attention to that as well.