I have no land now so there is no need for seeds . I do not have or want them at this time .
My goals were to cross all brassicas with the Giant varieties and also with the most extream conditions tolerant ( disease, drought , frost , resistant strains .
In cabbage there is OS Cross 65 pounds and I have heard of larger ones.
Then after I have a giant brassica that can grow anywhere and survive anything , I would try to breed in the high oil and protein content of rape seed , the taste of mustard seed , the leaf bud of the cabbage and its quick cooking ability the less smell of the collards , the root of the turnip , the stem of the kholrabi , the long keeping of the rutahbaga, the flower buds of the broccolli , or cauliflower the rapid growth of the bok choy ,the kale frost resistance and colors , and brussel sprouts and the best vitamins and resistance from all of them . There is no legislating taste , so that can be bred in later .

Interspecific crosses are not easy here. http://en.wikipedia.org/wiki/Brassica will give you an outline of the brassica species.
The link below shows a chart of some of the relationships between them.
I'd rather cross within a few species, as there is enough interesting genetic stuff present.

Here is a link that might be useful: {{gwi:992861}}

try this link
http://images.google.com/imgres?imgurl=http://waynesword.palomar.edu/images/cockap1b.jpg&imgrefurl=http://waynesword.palomar.edu/hybrids1.htm&h=365&w=424&sz=49&hl=en&start=9&tbnid=rJIr2atJTpJhkM:&tbnh=108&tbnw=126&prev=/images%3Fq%3D%2522animal%2Bhybrids%2522%26gbv%3D2%26svnum%3D100%26hl%3Den%26safe%3Doff%26sa%3DG
Also there is the "kholbaga " developed by the University of New Hampshire .