I picked one up from scalesgalore. The Adams brand are about $92 after shipping. Cheapest with shipping that I could find.
Something else you can also do if you have an already calibrated scale like an FX120 and want to save money is get one of the cheap class 7 100g weights that cost around $15. Then weigh it and put a tiny drop of super glue on the machined out divot on the bottom side to make it the correct weight.
One came with my Autotrickler. It was 99.997g. I added the tiniest amount of super glue and now it reads dead on 100.000g