[GreenKeys] What ribbon to use for Model 15

[vibroplex at mindspring.com]

Dear Friends,

I now have a Model 15 to play with.  It needs a ribbon and I hope at least one person knows a source for these?  Do any of the ribbons at the Office Supply stores work?  If not, where can I order one?

Thanks for any help you guys can give me!

73,

Derek
WB0TUA