Well, since it's often hard to guess exactly how many birds will come out of each hatch, I'd venture to guess they try to undersell their birds so that people aren't disapointed when their order can't be fulfilled. That would mean though, if a hatch went better than expected, or if someone cancles, the birds may be available for a given week. If you really want some birds, I'd try anyways!
Web links to Cackle and a couple of dozen other hatcheries and breeders can be found at www.CountryChickens.com.
For the record, I also got an email reply from Ideal today saying they're sold out until April. There are a couple of other Texas hatcheries, plus Privett, but I haven't contacted any of them to see what their availability is.