Once the clamp is pushed off the flange it's just about impossible to get it back on as the rubber is compressed when it's banded on originally. I had it happen on a nissan axle way back and I stupidly ended up ruining the boot in my attempts at trying to get it back on. You need to find some place that has the tool to put a new band on. If you know anyone with a 'gun' for putting on/tensioning plastic tie wraps, you could put a heavy nylon tie wrap on there to get by temporarily (very temporarily), just to keep the water/crap out of the joint 'til you hook up with the correct metal wrap/tool.