Getting a part time/weekend job

I'm in my second year of sixth form and I intend to go to move away to uni next year, but I don't get EMA and I need some source of income at the moment. I need to get some form of job, but I do a lot of music and band stuff outside school on top of my schoolwork, so although I have some spare time it's all like a couple of hours dotted around and maybe 1/2 nights a week. A lot of the weekends I have concerts but they're not on regular days, sometimes Saturdays and sometimes sundays, some afternoon some evenings. Also my school has a 2 weekly timetable so alternate weeks I have different afternoons free.
Is all this going to make it nigh on impossible to get a part time job, or am I just making excuses? If so any suggestions for employment from now till the end of summer when I go to uni?? I need something I can get money from that won't compromise my schoolwork as I need 3 As for uni!
Any help please!?!