I have always used a couple of BB's in my Testor's Enamel paints, and that has worked out fine for 40+ years. But lately I am buying more and more Tamiya Acrylics for the variety of colors. I stir them before each use, but it doesn't seem to mix the pigment enough. I hand brush. Any suggestions or hints much appreciated!

I use hematite beads (which you can get at Michaels/Hobby Lobby). These are a type of iron oxide, but cannot rust further, so there's no fear for rust contamination. Plus, they are very heavy...great for mixing paints.

However, it's always worth having an old paintbrush to mix the acrylics in the jar, as well as in the airbrush cup.

Spend about $10 bucks for one these and you'll be set. The motor in mine went a year or two ago, but I was able to replace it for cheap by getting a new motor at the LHS in the area.

https://www.amazon.com/Ammo-Mig-Jimenez-STAINLESS-MIXERS/dp/B00Y968LH0/ref=sr_1_1?ie=UTF8&qid=1472142045&sr=8-1&keywords=ammo+mig+balls

or
https://www.amazon.com/gp/product/B007B2AH7Q/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

I found it therapeutic as well as finding dried out paints.

I use the badger-type mixer as well and it works! I think the essentials for using tamiya and GSI paints are the paint mixer and the Gunze bottle grip/opener.