If you're an international student they don't expect GCSEs. They will consider whatever 14-16 education you did instead of them; if you didn't cover the same core content however they may have an issue, but most education systems will cover roughly the same content as the national curriculum at that age anyway (albeit usually in a slightly different format).
You should check with universities you are considering applying to in order to see whether your choices are suitable. Some may have issues with e.g. taking Maths Studies or whatever, but I think most won't be that fussed provided you do well in the courses you are taking for law.
Out of curiosity, why are you taking Physics HL and only Maths Studies...? It seems a bizarre choice not to at least take SL Maths with Physics in IB...