There are some forestry association’s that are still selling Christmas trees in the last few days before Christmas:
The Árnesingar Forestry Association is holding a Christmas tree sale in Snæfoksstaðir until 23 December, 11-16. See: https://www.facebook.com/snaefokstadir
The Eyfiirðinga Forestry Association has a Christmas tree sale in Kjarnaskógur until 23 December. See: https://www.kjarnaskogur.is/jolatre
The Hafnarfjörður Forestry Association, at Gróðrarstöðin, Þöll, on Kaldárselsvegur until 23 December, 10-18. See: https://www.skoghf.is
The Mosfellsbær Forestry Association, in Hamrahlíð until 23 December, 12-17 every day except for Þorláksmessa, which is open 10-16. See: https://www.facebook.com/SkogMos/
See also: http://www.skog.is/jolatrjaavefurinn/