Malistaire drops random items. The chances of you getting exactly what you want are probably about 1 in 25. That means you could get it on the next try or not for the next 100 tries.
I've read that some wizards have good luck with Malistaire's (Crowns) chest on the very first try. The general strategy is to try the chest exactly once, for 50 crowns. If the desired item isn't received, you should wait 24 hours so that the chest price resets to 50 gold. In the meanwhile, the item you do get may be useful to another of your wizards, or it can be sold at a shop for a decent price.