It looks like you need to focus on how to sort your data to group your records by 6 month ( and larger ) periods instead of how to perform a find as you want all the records, but with subtotals for each time interval.
My first question is about those intervals. Do you want to use the caledar to designate the intervals, a date in the table, or a date specified by the user?
Date by calendar. 1st 6 months is Jan 1 through June 30. Second is July 1 through Dec 31. 12 month total is all records with same year, and so forht.
Date in table. 6 month interval is all records within 6 months of oldest date in found set.
User specified date: User enters a date such as June 15, 2012 and that's the first day of the first 6 month interval.
And do you want to list indicvidual records within each interval or just the Bi-Annual totals?
My best guess is that you'd want the first option with a report that looks something like this:
Jan 1 - June 30, 2012 Total
Jul 1 - Dec 31, 2012 Total
Jan 1 - June 30, 2013 Total
and so forth.