A couple more thoughts ... (When I 'talk' about the Circuit Finder idea, I'm assuming you have breakers -OR- the tool can work with fuses as I stated in my original Follow-up.)
IF the light is on its own line as you say, then with the light switch in the OFF position, you could 'drop' the fixture out of the ceiling and temporarily wire-up an outlet, and then use the Circuit Finder tool. Of course, once you've located the breaker, you label it. Be SURE you have a volt meter w/you to TEST the fixture BEFORE you drop it out of the ceiling. Hopefully, the fixture is simple enough that there are HOT, NEUTRAL, and GROUND wires ONLY. If there are more, I can't say what the setup is.
IF the above can't be done (safely that is), an Electrician is most likely to simply SHORT out the circuit. I DO NOT RECOMMEND this unless you know what you're doing. But it's an old Electrician's trick.
There is one last idea. IF you can find someone with one of those screw-in outlet adapters for light fixtures, simply screw one of those into the fixture, then insert the relay end of the Circuit Finder tool. I don't think you'll find this 'adapter' in the stores. I'm not sure they're Rated. My Dad has one but he got it YEARS ago. AT worst, find a friend of a friend, or a neighbor or someone who's comfortable with electricity, then run these 'ideas' past them.
Other than that, perhaps others have some thoughts. (Stick around for a few days to see what 'they' say.) My best to ya and hope this helps.