You'll need to look at the international brokers. Try IB or Saxo.
Merkur Market is a multilateral trading facility and was established in January 2016. The market place is not subject to the Stock Exchange Act or the Stock Exchange Regulations. Merkur Market is best suited for smaller and medium-sized companies or large companies that do not satisfy the admission requirements or do not wish to be fully listed on a regulated market. ( ref Wiki)
Now that I know the Merkur Market is for companies not listed in the main Oslo exchange. I doubt any broker, other than those in Norway would bother offering access to it.