Up here in North Texas the rule of thumb is usually to apply it in the last week of December. You want to catch the coldest time before the new growth is starting, but if you don't have much frost or freeze activity it might not work quite as well. I think you're in the next hardy zone up from North Texas, and without as much cold it may be more difficult to catch that dormant period. By February I'd guess it would be too late.
In Austin you should have plenty of stores selling it, and you'll find a granular and a powdery type. You can keep it, but it does attract mice and such.
Howard has a directory for finding businesses that sell organic. It is this page:
http://www.dirtdoctor.com/organic/garden/advance_business_listings/ and just enter your city and you'll find several. I see lots of them showing up down there.