Kil: I googled the exact phrase: "8 oz bucktail" and got 639 hits. (Of course a lot of those were such items as 1/8, 5/8 etc. but some were for 8 oz heads. Of course, I doubt the quality of those would meet your standards as to hook quality etc. Another option--you may have thought of it--would be to have a custom mold made to fit the specific hook and body form you want and make your own. Do-It molds makes a blank that you can have machined. I realize this would not be ideal, but only an option if you can't find what you want easily.
I have explored this option for designing my own 4 ounce casting spoons until I found an existing mold that was close enough for government work.
One firm selling the blank mold is Jannsnetcraft,
Do-It blank molds, make your own custom molds Some others are Barlows and Stamina. I believe that Do-It actually charges more than their distributors to encourge buying from them. The largest actual (pre-made) bucktail mold they carry is 2 ½ oz. They point out that custom machine work is expensive so to check on cost before buying the blanks mold. I think this mold is less than 6 inches long so may not be big enough for that size jig/hook.
Russ