Check out musicmentals posts in teaching and lecturing, i did music and maths physics (as a minor) in ucc.. Not enough modules to fit with tc for maths so might do an open university add on..any jobs i des offered for music are part time and low hours so the maths might be a handy option for you to pick up the slack... I.e. take the 5hours a week offered by the school but make it known that yould be willing to do some maths or maths resource classes...
Any permanent jobs its usually music and irish, or music and religion,
maybe log on to educationposts.ie and have a look at jobs on offer and subject combinations required
As regard s courses these days I reckon it can be the extra curricular stuff that might swing it for you in an interview so get involved in other things too