Chances of getting TA/RA position

Hello,

I have been accepted to Masters program in Geoinformatics and Geospatial Intelligence for the Fall 2017. I have tried reaching out few professors for RA/TA positions and haven’t got any positive feedback. Most of the RA positions are already filled and TA positions are usually given to those who have taken a course previously at GMU. I am an international student and looking for means to waive my tuition.
If I join in Fall 2017, what are the chances I could get TA/RA positions for Spring 2018. Is it difficult to obtain part-time jobs for International student ?