Some foreign companies are, but they're usually listed on Exchanges in other countries still.
For example, Vestar (VWSYF) or Nordex (NRDXF) are both OTC in the US, but they're also listed on Frankfurt Exchange, Xetra, OMX. Both are large companies, Vestas has 35% of world market share in wind turbines, Nordex is there with 20-something %. Vestas is at over $100/shere, Nordex is somewhere in $30's.
The usuals, whatever I post is my opinion, yaddayaddayadda. I'm still learning this, so if you listen to me, well, good luck to you :)