BeerBorg

Is it possible to make Sours from extract?

Yes. Don't matter how you make the wort. Just add a handful of urn rushed grain and keep the wort temp at 120f. I did for 18hours got a nice sour brew.

Damn auto correct un crushed grain

Yep, you can toss in some uncrushed grains into extract wort @ 140* and cover the wort so that no air can get in. Lactobacillus lives on grain husks and does not need oxygen to reproduce. This is how sour mashes are done.

You can also get liquid lactobacillus and/or brettanomyces and add it to the wort at fermentation. They are a wild yeast that produce lactic acid and will ferment wort, but you will probably want to also pitch some traditional brewing yeast because the bugs will not attenuate wort as low as brewing yeast. The drawback to doing it this way is they will permanently infect plastic fermenters so unless you're using a stainless fermenter, you must use that fermenter (as well as any plastic tubing or utensils that made contact with it) for sour beers only from that point on.