field supports a maximum of 500 options

For efficiency select options are capped at 500 items but only when using the Options Element module. You can manually increase this by using hook_form_alter() in a custom module and increasing $form['items']['options']['#limit'] = 8000; Note that I expect that such a large list will cause browser performance problems both when editing the field and when trying to view the form.

I don't provide support on actual coding, but that should be a good enough start you can take it from there.