Here's one way how you can accomplish this through transmutation alone, and without the use of level 9 spells, before you can even cast level 8 spells.
From PHB 119
A 6th level Wizard, who is of the Transmutation School gains a nifty little ability to create a Transmuter's Stone. You must spend 8 hours to create the stone and the stone in question can have various properties that it bestows to the holder.
Once that same Wizard reaches 14th level, and only able to cast no higher than 7th level spells, it gains the ability to destroy the above mentioned Transmuter's Stone to use up the store of magic to permanently cause a 'Major Transformation' . You can Transmute a non magical object(s) no larger than a 5ft cube into another non magical object bearing the same size and mass and of equal or lesser value if you spend 10 minutes handling the object. Since "size" isn't equivalent to "volume", and density is another thing entirely, you just need a total mass equivalent to the metallic alloy you are aiming for as well as the original item(s) to cost at least equal to the metal you need.
Using this method you should be able to consistently make an abundance of the desired alloy in between long rests.