You won't be able to find it in any grocery
or chain stores - though you can find it in
"Independent Chains" (eg - I don't *think* I
saw it in PetSmart; I know it's not available
to PetCo, but Pet Club does carry it).  
I buy mine from a truly independent store near 
where I work, even though it's more expensive there
than at Pet Club, because I like what they do and 
want to keep them in business.
My girls were on flagyl (aka metronidozole) for
3 or 4 *months* in trying to get the diarrhea
under control.  I tried several varieties of
good food before finding the S.C. - and only found
that after browsing through and reading labels on
all the foods in several different pet stores.
The only one that comes close to it in what I
consider good ingredients is Neutro Natural - and
I don't use that because they don't have a light
or a canned variety.  I use the Reduced Calorie
dry twice a day, canned mixed with other stuff and
water once a day, and use the regular calorie dry
instead of "pounce-type" treats.  (BTW - this is
among 8 cats.)
S.C doesn't have corn, rye, wheat, or any of the
preservatives.  
If you have access to the Web, you can probably ask
them where the closest retailer is:
Diana