I can now bring this mystery of where the 105mm guns came from to a close. There was a third source of ship's weaponry in Narvik harbor: British armed merchantmen. Here is a quote from the book Hitler's Pre-Emptive War page 290:
"...The five British armed merchantmen in Narvik harbor on April 9 each carried two 105mm guns. These were brought ashore and two were mounted on rail cars. The sailors were also active in getting the railroad back into operation...…"
Thanks to everyone who added comments to this discussion. Your info helped me to narrow down possible answers. The Norwegian patrol boats may have been also stripped of useful items, but they were not the source of the 105mm guns