Crafting it can be a heavy cost, as it costs Resplendent Sparks and a handful of rare runes, which you can only get in certain ways such as completing the Season rewards and increasing your reputation with the Zakarum Remnants. You can also get it by Diablo 4 Items salvaging other Mythics that you may not need.
The other way is to get it from the Mythic Unique is to get it from the Mythic Cache which you can craft from the Blacksmith. This however also costs Resplendent Sparks as well as 50m gold. This on top of the fact that the Mythic you get is completely random is not a great way to spend your Sparks or gold, so we wouldn’t normally recommend it.
The only other way to farm Uniques is to just continue with content. Unfortunately there’s no easy way to target farm Uniques. Currently, Uber Bosses in Lairs on Torment 4 have around 1.5% chance per item roll to drop a Mythic Unique, so roughly 7.5% chance due it five items being rolled. This chance is low but as with all randomness in the game, can be overcome by continuing to run the content.
If you’re lucky enough to get your hands on cheap Diablo 4 Items this item, be sure to use it wisely and good luck!