I'll take a stab at this, although others may have more precise information.
Nationals are the same time every year. Their locations are decided a year and a half before the event. For example, the 2009 championship locations were decided last December. Except Gold, they are in OKC every year.
Metros, Regionals, HOF qualifiers, and state qualifiers are usually posted on ASA's site starting @ February and can be found here:
http://www.softball.org/tournaments/tournaments.aspYou also want to browse your local/state associations site. They will have your local flow chart as to where the qualifiers are, dates, and how many berths will be awarded. For example, this was for TX this year:
http://www.txasa.org/flow_charts/2008/14ua.pdfFinally, continuously search VTD in late winter-early spring for tournament postings and sign ups. You can also search through prior years to get a guesstimate on the time frames for next year, most are May 1-July 15th.