Yamaha yst-c11 speaker cables needed/ or alternate

I picked up at a thrift store a Yamaha yst-c11 which was $1000 system back in the early nineties but it came without cables
there is a specific mount on the component body for the speaker cables that resembles the following "diagram"

L R
.| |.

I've tried inserting regular copper cable to no avail
the speakers themselves are standard red and black suited to insert typical cable

is there a source for these?
I have found nothing on line
Yamaha also made a home theater system with the same model number and everything online relates to that
is there a bypass solution to get this functional?
Thank you
Alan