wider laced wheel

I recently purchased a 78 KZ 1000 a2, I want to go with a wider laced wheel like a 18x5.50. but when I try to find any that fit only Harley pop up. then says no compatible. any help would be great also I have 82 gs1100e swingarm.

The biggest rim that will fit that swing arm will be a 3.5" x 18" with a 150/80 x 18" tire if you can find that tire size any more. You may have to settle for a130 or 140 width tire. A 130 wide tire on a 3.5" rim will fill up that swing arm nicely.

I run a gs1100e swing arm on my 77z1000 A1, it has a gsxr750 rear wheel running a 180 back tyre. theoretically you can find a Harley 5.5 aluminium 40 hole centred rim and lace it up but...you will e running into a fair few problems. The chain clearing the tyre for one, you will have to make a spacer to shunt the sprocket out to clear the tyre and an offset front sprocket to bring the chain out to be true. Problem will always be cause and effect, every change will have an effect that also needs to be changed untill its all right.

The GS{X}  1100 swingarm was made for a 17 inch rear  wheel, I have a 4.5 x 17 rear mag that fits in nicely, you won't want  anything wider than a 150/160 rear tire depending on manufacturer as the widths vary .. . There are plenty of 17x 4.25 spoked rims available, that would be fine for the 1100 swingarm.
If you're using a stock hub, chain to tire clearance  will be tight...  Measure everything meticulously ...