If you can't find the stripper Tonar used, what you want is something based on Methylene Cloride or Dichlorethylene. Polyurethane will laugh at most other strippers.
There's a chance, albeit very thin, that you have a lacquer finish. The way to find out is to put a drop of acetone someplace you don't care about, like inside a control or pickup cavity. If it's lacquer, it'll melt. If you don't have any acetone around the house, nail polish remover is usually 99.9% acetone and .1% aromatics.