If I filed a request for an extension on my federal return on the 15th and was notified it was rejected and to resubmit my request ,where do I find the form?

You can't submit an extension request after the deadline.  Normally, if your e-file was rejected due to mis-matched information, you would have 5 days to correct and resubmit, but I don't know if that applies to extensions.  If you did not see the link to submit an extension, then it was removed because the deadline passed.  At this point, just file your return as soon as you are able.