Will this suffice?
I know NX sells -8 to -6 and I believe -8 to -4 adapters. (they sell them for that giant bottle valve they make which is a -8) Then you could run a -6 or -4 if your really set on running a smaller line.
Otherwise Nitrous Outlet sells the braided Blow down kits which already has all the fittings you need.

Cutting those hoses and putting the blasted fittings on them is a real pain! Cover them with tape before ya cut the braided end and lubricate the hose ends to slip the fittings on.
http://www.dynotunenitrous.com/store...p?idproduct=86
Enjoy!
Dean

