When you say you have "maxed out supplies" Do you mean you have upgraded all you workshops to their max level, but need more supplies, OR, your supply storage is full? If the former, you can gain supplies in many ways (returning neighborly help, as rewards for various quests, rewards from buildings like wishing wells or other event structures, etc.) If your supply storage is full, then you can trade supplies for goods with the Wholeseller (part of the Trader).
Scouting provinces is expensive, and (arguably) is meant to be so. Be careful not to over scout, you will regret it later (via the dreaded Orc ring).