this one is half of your range at 10g max
ebay 10g / 0.001g LCD Digital Electronic Pocket Gram Jewelry Diamond Scale Silver
basically when you sort pellets, just make 3 heaps, light-medium-too heavy so you can use all. sort only one tin at a time. dont try to sort/mix more than one tin of pellets.
all you want to avoid shooting too light in a group of heavies or opposite: to have a heavy one in a group of lights
good luck
edit: really precise 'laboratory balances' are very expensive and the type you would really need is where you have to close the door on the glass cabinet to take a reading.
but there is no need for that, try the 10gram model, works even for .177 pellets -tested successfully. it is good enough for this job