Hi Conni, I know of several heat transfer T-shirt shops in local malls that also sell panties and thongs. Usually staffed by teens and twentysomethings, they will happily apply images or custom lettering to any garment they sell.
If you have such a shop in your town I suggest you put on a sexy outfit and ask any white boy behind the counter to make you some thongs that read Black Cocks Only or I (heart) Black Cock. :wink:
That being said I do know a company that makes a thong panty that reads Soul Food. Here's their link.