The 58 was a pretty rare model because of its high end design so your best bet it to contact TASCAM directly as they normally do keep these manuals in stock and charge approx. $30 buck for them.
TEAC America, Inc.
7733 Telegraph Rd.
Montebello, CA. 90640
USA
Phone: (323) 726-0303
Fax: (323) 727-7656