I doubt that you will find any information for this alloy in the T4 temper. It is supposed to be artificially aged to the T6 temper for optimum properties.
Why not build the S-N curve yourself as it is done in any machine design book using 0.9 of the yield strength at 1000 cycles and the 0.4-0.5 yield strength at the 10,000,000 cycles on a half log graph?
Yes, the fatigue life of alloy 6082 will be significantly different between the T4 and T6 tempers. If you do not perform testing on the actual material you have, then israelkk's suggestion is the best way to estimate the properties. Why do you want to use the T4 temper instead of T6?
I cannot choose what material to use; it is a standard material, available in the laboratory. If I don't find anything about 6082T4, I will have to approximate.
The whole fatigue calculation method is not so accurate. In the aerospace field ususally the spec requires a factor of safety of 4 to 10. Therefore, the approximated graph is almost as good as any graph you will find. All this without taking into account the quality of the alloy, the exact surface finish, exact stress state etc. which will add to the uncertainty of the fatigue analysis.