I have got both a 2010 and a 2011 Shadowcat. I can't speak too much about limbs, as both mine have Barnsdale limbs fitted, but with the 2011 model, the are not really necessary, just nice to have.
The major difference between the two is only relevant if you have a longer draw, as the Cat and Nitro 1.5 cams are identical, in fact, there is no difference between any of the 1.5 cams from the Hybrix onwards. The 2.0 cams are a different story, and pretty much all the 2010 model limb issues I heard about were with CAT 2.0 cams.
My 2010 model came fitted with CAT 1.5 cams and my 2011 model had Nitro 2.0 cams. I liked the Nitro's so much, I bought a brand new pair, which I imported to the UK and fitted to my 2010 bow.
So, in essence, if you have a shorter draw, 27.5" to 30.5", then you will be using 1.5 cams on either bow, so no difference at all really. If you draw 30" to 32", then you wil be looking at the 2.0 cams, and in my opinion the 2011 bow is the better bet.
AS for where to buy; watch the AT classifieds, I bought both mine from there.
Dedicated Finger Shooter.
Shadowcat(s) with Barnsdale limbs: Davis The System, Free Flyte rest.
Sky Art carbon arrows.