Just search ebay or better yet amazon where you can read reviews, they aren't particuarly expensive(at least I don't think so). You probably don't want to buy the cheapest one, sometimes they have trouble with really small amounts, like it could tell you the difference between 20mg and 19mg, but at less than 5mg it might have trouble being precise; or so I've been told. I would still suggest you make a solution and do volumetric dosing rather than trying to weigh out a single dose. Either just search for "milligram scale" or include "0.001g" the 0.001g is the common denotation for milligram scales.