You can get them through attitude seeds. I only have one experience to draw from and that is with Super Lemon Haze (SLH).
First the good: Attitude seeds has been very good for me. The package arrived in good condition and within 10 days. All five of the feminized seeds I purchased successfully germinated and grew to be adult plants.
Then the bad: Of the five seeds, I grew two in my DWC setup and a friend and experienced grower grew two in aeroponics and one in soil. NONE of them turned out very well. The high was ok. Not killer, not awful, but did have a good taste. The flower time was fairly long (75+days if I recall correctly). Lastly, the yield in all three mediums(DWC/Aero/soil) was horrible. To put it in perspective. The freebie seed I got with the order (Blue Venom), yielded three times as much and actually was better bud in the exact same DWC setup.
I'd like to think my friend and I did something wrong, but we've each grown for long enough to spot deficiencies, pests, etc... and all of our other plants (Blue Venom, Blue Cheese, and Casey Jones) turned out much better and higher yielding than the SLH.
Lastly, Arjan is huge on winning the cannabis cup. This sells seeds. Keep in mind this competition is hardly objective. Arjan hands out wonderfully packaged bags of his entries and is very generous with them. For this, you gotta give him credit. The guy knows how to market cannabis. From the packaging of his seeds, to the giveaways at the cannabis cup, to the professional photos on the website. It's driven like a class act. Sadly, that doesn't always add up to the best of the best. In my opinion from both smoking it in Amsterdam and here, Barney's farm stuff is hard to beat. I seriously think the highest I've ever been in my life was after sitting in Barneys smoking an entire spliff of "Laughing Buddah" with my wife.
Hope this helps. Again, just one guys experience with one seed company. So take it with a grain of salt. I just personally won't probably order from them again.