AJAX Truclient checkbox selection for same set

There are two different set of checkboxes (InStock & outStock). 

Business flow is to select all the Instock checkboxes on the page(Instock checkboxes numbers will change with different user) and click next button on the button of the page.

Could you please let me know how to select all the Instock Checkboxes and move forward.

Please find the screenshot attached.

Regards,

Sai