Park Seeds has them see link below

Here is a link that might be useful: Seeds

When you look up "black peppermint" you find the the plant Eucalyptus salicifolia. Do you mean peppermint or this eucalyptus variety?

FataMorgana

If you could find someone that can give you cuttings of a peppermint you can smell/taste and find that you like, it would be better than seed since mints cross with one another readily. (Although I expect Park seed is trustworthy.)

Hi! I have also been in search of Black Peppermint - yes, Mentha x piperita, but it is NOT the one at Park's. The one I am looking for can be found below at Marshlands (halfway down page).

Peppermint Black Mentha x piperita
A darker form of peppermint, with glossy dark green leaves and purple stems. Black peppermint is native to Tasmania, it's the variety usually used in peppermint tea as it has more essential oil than standard peppermint. 18ins (45cm) Plant: �1.70

I had my plant about 18 years ago when my son was first born from a small nursery here in Texas - though I call them now and of course, they think I am crazier than a loon. If anyone happens to have some growing, or knows of someplace to get some stateside, please let me know ;)

mizu

Here is a link that might be useful: Marshland Herb Nursery