I called Roland in California and they were able to send me an XP-50 manual for 9 bucks. I suppose they would send you one for the JV90.
I got their number from the web-site.
Corporate Offices
Roland Corporation U.S.
5100 S. Eastern Avenue
Los Angeles, CA 90040-2938
P.O. Box 910921
Los Angeles, CA 90091-0921
Phone: (323) 890-3700
Fax: (323) 890-3701
If I remember right, that number was the one I called and ordered my XP-50 manual.
Peace,
Bob