That is something why the inventory is kinda not finished yet, i was thinking on places like the campaign or other modes that you would get more items along the way.
But it is not implemented now, i think is worth it to think about it once i have more progress in the campaign.
The only think done atm is the secret cube that after 60ish pulls with no SEC card would give you one that allows you to buy one SEC directly. (I am sorry though, as you cannot buy them with SEC cubes yet)