Try: http://www.badmintonsupplies.net/f1store.html Call them, I think they have black BG65 back then.
you could also try ebay... i bought all the black strings off one of the sellers... BG70pro and BG 68 Ti.... there is also another seller who is in Covina who emailed me if I wanted black strings... he offered me 5 BG68 TI black for 35 shipped... email or PM me if you want his contact... i am not sure if i can post it here... Calvin