It should be possible to make a two pole 240V GFCI that does not require a neutral for power, and is intended only for use on a two wire 240 circuit, but that does not mean that any manufacturer would choose to make one.
In earlier threads the possibility was raised of synthesizing a neutral using the center tap of a 240V winding. But although it would operate correctly it would not be Code conforming.
A European style pure 240V breaker with GF trip (RCD) would probably work, but it may also expect one of the lines to be at ground potential.
The fact that the NEC requires GFCI (as opposed to GFP) only for up to 240V, makes it reasonable for manufacturers to concentrate on 120/240 applications only.
