As far as made in the USA I don't think you will have much luck. if you want an accurate electronic scale be prepared to pay for it. FX-120I are supposed to be really great and can be had for about $600. Sartorius is another well respected brand but also pricey. Both of those use magnetic force restoration technology not load cells or strain gages with anti drift algorithms . Otherwise any electronic that uses load cell technology are about all the same and accuracy will be plus or minus .1 grains. Some may be assembled in the USA but all will use circuit boards form China. You can pay anywhere between $19.95 to $200.00 for one.
here is a video showing the difference
https://www.youtube.com/watch?v=zxMz...ature=youtu.be
or you can get accurate and cheap with a accurized beam scale. Watch a couple of this guys videos to see how
https://www.youtube.com/user/thetargetmaster/videos
actually since for what you plan to use it for a $20 scale off EBay or Amazon should be plenty accurate. Not meaning that as a slam but the accuracy of a product will be limited to the least accurate mechanism in the process, in this case the powder throw. I made a few thousand rounds of pistol and plinking ammo using the same method and they all were fun to make and shoot. Just saying that instead of a expensive scale a average one will do and spend the rest of the money on powder and bullets. Trigger time helps everyone improve their shooting ability