It seems as though you are trying to replicate the find button exactly. This can not be done exactly. Although you can create a series of buttons ( or one button that could prompt multiple choices) that can create a new find and modify the last find, there is no script step to save or edit the found set.
That being said, you may be able to use an advanced technique to store your previous find criteria in records in a table though. One such as : http://www.nightwing.com.au/FileMaker/demos9/demo903.html
Thanks... your info helps me better understand.