green thorns you pay from players vendors. They are not that expensive. Once you buy a few, take them to a dirt patch (not sand or a field these cause different effects) use them a fountain of regs will spawn.
also you know that you can "build" a 100% lower reagents cost suit, so you use no regs when casting spells. the downside is that usually the resists on this suit sucks, so you have to find/replace/craft pieces to fit in. Usually people try to build the "perfect" mage suit which would be 100% lower reagent cost, 40% lower mana cost, 18 mana regeneration with all resists at 70.
also if you use a warrior save the regs from the monsters you kill, its not much while you are out hunting, but if you just throw them in a container in your warriors bank and check them after hunting every week, they add up. Also I save all my regs from my gm fisherman when he fishes up treasure chest.
Do you have a house already? If so and it not a castle or keep try to find a spring decor token. Use it to claim the blessed statue, which when secured in your house will spawn regs everyday, now yes it just one reg pile (example 20 blackpearl) everyday, but again they are free.