Place a buy order.
I regularly buy 100-500 million units of trit at a time. At times I have placed buy orders for a billion units or more (this being the rare occasions I’ve done large scale building of pirate faction battleships).
I just post buy orders in backwater stations near where I intend to use the trit (same system or at most 1j).
There’s no point mining. Even if you manage to avoid losing ships, you cannot compete with highsec mining bots, nor can you compete with null rorqual fleets.
I do the same for Pyerite and Mex. Other minerals that aren’t Morphite I purchase in hubs and carry by deep space transport. Morphite I just buy a quarter million or half million units, then set a collateralized courier contract up to get it moved.
If you have outstanding refining skills and access to an Athanor or Tatara, you could also consider buying compressed ore in Jita. Generally this is not worth it unless you are running a large scale capital ship construction setup.