cb360 swingarm swap or extension kit?

So earlier this year I decided to build a vintage bike for speed week 2015. I am finishing work on the frame, and all the carbon composite bits and pieces. I am down to the swingarm and am having a bit of trouble finding a suitable extension kit or viable swap for the bike. I plan on pushing the rear tire out 3 inches possibly up to four. Wrench tech racing at one point sold kits to extend the swingarm, but on every ocassion they seem to be out of stock. I contact them, but to no avail. If anyone has a bit of info for me I'd be greatly appreciative.