As far as I know the owner of the private blackseed forum has links to some outstanding blackseed products she is affiliated with. Other than that source, I would suggest looking at iherb.com. They have wonderful prices and service and a very wide variety of sources.
I order lots of supplements from them. If you can find someone who has ordered from iherb before they should have a referral code to get you $5 off on your first order. I have one myself, but posting it here in a public forum would technically be a no-no (I get a small referral fee when it is used, which I use to offset out purchases).