When I first moved to Norway I was convinced these places didn't exist. It turns out my husband was just the wrong person to ask. Many thrift shops go by the name of gjenbrukt and often people advertise for their own personal garage sales as well as school fundraising in the form of a flea market. There are also Fretex stores scattered about for people to purchase used items from. The word antique in Norwegian is antikk, very similar to its English cousin's word antique.
One thing I love collecting is foreign coins. I've been collecting them since I was a little girl. So of course this is one thing I try to look out for when I am at a flea market. I was pleasantly surprised the day I went to a flea market for a school fundraiser this year. I brought my daughter with me and she wanted a toy cash register. I bought it for her and when we came home and she hit the "cash" button she shouted, "Mamma! MONEY!" There was a mixture of play money and real Icelandic money and a euro.
Mainly I just buy things for Pia when I'm thrifting. I've found a nicely used dress for her earlier this summer for about 10 kroner or $1.50 USD.