It might be a little difficult to find seeds now, but generally stores that have any type of gardening section will sell catnip and cat grass seeds. They do sprout and grow fast.
One thing to remember, be very careful what type of potting soil you use. Some have fertilizers premixed into them. A simple solution to this is to use a sterile top soil mix - again this may be difficult to find in stock in November.
I buy mine from the local feed store or garden centre, I can grow them a lot cheaper than the $4 a tub they sell for around here and the home grown ones don't wilt as quickly as they haven't sat in a store or been transported for a few days before the cats get them