If you want to get a collection of all tables which starts in a text frame you'd do something like this:
myTextFrame.tables. However, this will not find tables continued from a previous text frame. For that you need to work backwards and infer it from the textframes the table occupies (assuming there is one).
For InDesign-specific questions like this, the InDesign Scripting forum is a better place to ask: http://forums.adobe.com/community/indesign/indesign_scripting