I've used Schmetz in mine. Are you positive you are threading it correctly? I have had mine since March and never had to touch the tension at all for any thread that I've used.
Here is a source for Organ Needles. I haven't ordered them yet, but probably will in a month or two when I run low.
http://www.ctsusa.com/_e/Singer/prod...S15x1/15x1.htm