The U-3000 monitor is a current production model and the manual is under copyright. The ONLY source is to call Wells-Gardner and order it (1-800-336-6630).
Here are the part numbers for the various sizes/versions of the U-3000:
069X2815-100 (14", 17", and 19" CGA)
069X2812-100 (27" VGA)
069X2926-100 (33" CGA)
069X2868-100 (33" EGA)
069X2876-100 (33" VGA)
069X2950-100 (39" CGA)