I know you contacted HGTV, but they should be able to get you the SPECIFIC info as to the name or number or whatever of the show. Maybe their 'store' has the tape. If you can find out the show, as you know, obviously you can get the tape.
BUT, if contacting HGTV totally fails, try E-mailing *** **** with the info you stated above. I don't know what you can expect for a turnaround in a response but patience is a virtue. ******* hasn't been here, well, who knows!