pressure transfer from Grainfather conical fermenter to keg

[hoppyscotty]

Getting myself set up to pressure transfer from grandfather conical fermenter to a keg. My plan is to pressurise from the top and draw out from the tap underneath So I bought a try-lock fitting with a barb for the top and regulator and Sodastream bottle and adapter. However the size of the tri-clamp barb is quite large - about 13mm at the widest part of the barb. On the regulator side I've got a much smaller barb that fits the normal kind of gas line 3/8" I think. So I've ordered a 12mm to 6mm barb coupler to reduce the larger gas line from the grandfather end to the smaller gas line at the regulator end.

However I'm struggling to find gas line of large enough diameter for the grandfather end and the 13mm barb. What kind of line can I use at that size? I need something with about a half inch internal diameter.

Thanks