220v hot glue gun with Great Britain plug to be used in USA
You could just try and see if it works (gets hot enough) at 110 V.

The teardown of a gluegun by BigClive reveals that the heating element is a PTC thermistor which means it regulates its own power to maintain a certain temperature.

At 110 V the maximum power (when the PTC is cold) will be lower (compared to when used at 220 V) but after heating up the power required is lower anyway.

So I would just try and see if it works and if not, buy a new glue gun, they're cheap.