This one appears to be an 18/15" which is the smallest size that GT made. I've been looking for one in this size stateside for 5 years and there's only ever been one for sale and that guy was too stubborn to drop it at a bike shop for packaging even after I offered him a premium price for it. Someday...
The pile of wire beads in the lower left is all NOS 700D's and all three of my 700D bikes are wearing new rubber. They are out there and not that tough to find. One just needs to contact dealers that sold GT's in the mid 90's The are really quite a few around...just start emailing shops and you'll be mildly surprised. Especially if they are older Schwinn dealers that sold GT's. Old time Schwinn dealers are pack rats