Although X-20A is the thinner meant for Tamiya Acrylics, it actually thins better with Tamiya lacquer thinners (same bottle as X20A but with the yellow top). No idea why the "wrong" thinner works best but it does - gives a much smoother finish without graining.
It isn't as available as the acrylic version and I had to order mine from HK -
http://www.luckymodel.com/scale.aspx?item_no=TA%2087077
I've not tried it with Mr thinners but I believe it also works well (there are different types though including a lacquer type).