I don't see why you wouldn't be able to get more, part through garrison like normal, part through gathering.
What other people can gather through their garrison isn't going to match someone going out and intentionally herbing or mining. The disparity will likely be similar to being a gatherer vs growing things on your farm now.
But mainly the "use" for having gathering materials is that they cost nothing to level and create materials that are, at worst, useful to your alts and at best, money makers. If you already have one of every crafting, there's no reason to have more now that the combat perks are gone.