While this part was a US stocking part at one time, unfortunately it has been completely obsoleted through Mitsubishi... meaning there is no US warehouse inventory, no dealership inventory, no inventory in Japan warehouses allotted for US sales, and zero intention of replenishing stock.
Once Mitsubishi labels an item as obsolete there is no return to regular stocking; the one exception to this is if the part is a high demand part (for example brake lines or transmission on a collectible model) they sometimes will release vintage parts... these are often slightly used (demonstration parts, or dismantled from zero mile display cars etc) or imported non-US allocated parts. However again these are only done on high demand parts.
MD305949 being a structural engine bracket (not a part that normally is needed over the course of a vehicles life, short of accidents anyway), this pretty well rules that out entirely... and compounding that is that the part was never a US installed part, they only stocked them here for a convenience to a few Canadian vehicles and Mexico models (done regularly for convenience to those who import or travel while under warranty).
Unfortunately, there is basically no chance of finding a new one in the US, and finding a used one is not likely either since this part was not used on any US sold vehicles.
I think the best course of action is going to be the long road ahead of trying to contact salvage yards to find the part by model/year and hopefully find one that will pull it off the engine (potentially leaving them with a hard to sell engine missing that piece) and ship it. Given the model, Australia will probably be your best shot for both finding one and willingness to ship abroad.