(setq org-agenda-files (list "~/org/)) has a missing closing ".

Also, check out https://archive.org/details/gnuplotinactionu0000jane (Gnuplot in action : understanding data with graphs)

If opening a file is a problem, you can create temporary buffer and then use insert-file-contents + search + erase-buffer.

You can simply loop over all the org files, open one by one, and search within each file individually using (while (re-seacrch-forward …) …).