Hi Adam333, regarding a refractometer I purchased a Prim II by Presidium from Paaz Inc. (www.paazinc.com). for $291.00 brand new and it is helping me a lot in identifying different type of gems. It does help to have a little experience towork with it, but it is handy. It has a CD to load to your laptop to get the readings. As far as a carat scale, Paaz instruments may have them. Check on line.
Regards and good luck with your IGS certification course.