I know this is going to be very ambitious but I want to use copper tubing. I know that aside from Koolance, there aren't too many copper tube compression fittings out there, however I'm trying to work out a theory I thought of. Use fittings intended for 7/16 ID tubes, and use 1/2" ID copper tube. There will be 1/32" all around in between the copper tube and the the barb. Use a couple of appropriately sized O-rings around the barb, stick the copper tube in, and use the compression component to fully secure the copper tube.
I had these fittings in mind: http://www.frozencpu.com/products/16643/ex-tub-1340/Monsoon_Free_Center_Compression_Fitting_-_716ID_x_58OD_-_Single_Black_Chrome_FCC-71658-1P-BC.html?tl=g30c569s1763
I've ordered one to play around with. I will go next week to homedepot and find the copper tube I saw online.