[If my math is off here, feel free to correct me.]
I recall that there's a little less than 3 months between Chapters 2 and 3... so with a Prestige of 3 and assuming they have no Uncommon/Rare items already, they should easily be able to get 4 Uncommons (each), possibly more if they make checks.
Whenever you're requesting a new item for a character who already has at least one, the Favor Rating (and thus the waiting period) increases. If they only call in one favor to that one group per day, they can get outfitted with Uncommon items at a rate of one per day, for the first 2 items per party member (so 10 days for a default-size party). After that, each item they request takes a full week to show up, though I assume they can keep requesting new items while they wait.
Putting in requests for the third set of items only takes five days, but getting them will take 11 days. Now we're up to 21 days. Requesting the fourth set of items takes another 5 days, but appears doable on days #16-20, so the items will show up on days #46-50, which is still far short of Autumn 1, the start of Chapter 3.
Beyond that, they can't get more without making a rather impressive DC 36 Diplomacy or Intimidate check, once for each of the five next items.
... Of course, this is assuming they only go after Uncommons. If they go after Rares, they'll be able to get up to 2 each, with 2 Uncommons as well, before needing to make similar rolls.
So really, the more limiting factor here is their funds.
My party thinks the Prestige system is complicated. I can't imagine why...
I'm mostly done with Chapter 3, Act 1 at the moment, and my party has slightly less than 2 non-Commons per PC, if you want a comparison.
