It´s very easy to make them at home! Give it a try!

You can find the recipe in the following posts:
http://www.jamieoliver.com/forum/viewtopic.php?id=30787
http://www.jamieoliver.com/forum/viewtopic.php?id=30212
http://www.jamieoliver.com/forum/viewtopic.php?id=36154

Preserved lemons

Ingredients
5 (about 600g) small to medium lemons
145g (1/2 cup) sea salt
375-500ml (1 1/2-2 cups) fresh lemon juice
Method
Wash and dry a 1L (4-cup) capacity glass jar with a plastic or plastic-lined lid (a metal lid could corrode). Wash and dry lemons to remove any surface dust or dirt. Scrub the skin to lift any dirt or grit that is hard to remove.
Cut one end of each lemon, about 5mm from the base, so they sit flat. Place 1 lemon at a time, cut-side down, on a chopping board and cut lengthways into quarters without cutting all the way through to the base. Repeat with remaining lemons. Place the lemons, in a single layer, in a freezer bag and expel air. Seal and place in freezer overnight. Remove from freezer and transfer to the fridge to thaw for 6 hours or overnight. This helps soften the rind and speeds up the maturation process.
Fill each lemon with as much salt as possible. Salt extracts juice from the lemon, softening the rind. Push lemons into jar. Sprinkle over remaining salt.
Pour over enough lemon juice to completely cover lemons. Seal, label and date. Place in a cool place, away from direct sunlight, for at least 4 weeks. Once lemons have settled in jar, you might need to add more lemon juice to ensure the lemons remain covered. The lemons will start to soften and might start to float. As a result, they may not stay entirely covered with juice and may develop a harmless white mould.
To use, remove a lemon from brine and rinse under cold running water. Pat dry with paper towel. Use a sharp knife to cut flesh from rind. Discard flesh. Cut off white pith from rind. Discard pith.

Don't know but I wouldn't chance it.  Salt is cheaper than lemons.