Is there a tool that can clean the fins of a base board heater?
Like most projects, the undertaker isn't limited to just one tool. You have plenty of options to get those heat-sinks cleaned up. 

If the heaters are really as old as the house foundation, which is likely considering this was a convenient heating method for older homes (pre-1960), first you need to remove the front cover. You might have already done that since you are able to navigate the vacuum nozzle into the heat sinks which I can't imagine doing with the panels still on. The vacuum should be used towards the end of the cleaning process, which is great to pickup loose material, but not so much to "pry" off this build up of dust in question.

Sure, you can use a small little air can, but I would save that step towards the end as well for some detailed cleaning. But to get the bulk of the debris out, I recommend a portable air compressor with a Pistol Grip Blow Gun. Similar to the air can, but with much more pressure and focused aim. If you don't have a portable air compressor, it's definitely a good investment and you will find many uses for them. Many compressors on the market today either come with a set of attachments or can be purchased separately.

For safety, of course make sure no one else is in the area, and that you wear a face mask to avoid breathing in any debris. Leaf Blowers aren't recommended indoors if they are gas powered. Even electrical leaf blowers aren't recommended as the air has a much wider landing area and they don't have as much power as one would expect.

Also, before attaching the front cover (and possibly side covers), if you notice that the fins are severely out of shape, you should use an appropriate tool to straighten them out if possible. Doing so is very easy as the fins are very flexible, hence the reason why they might be out of shape. But it may take some time straightening out fin by fin. The purpose of doing this is to provide a better heat transfer and better, well, radiation. But if they are just very slightly bent, you shouldn't worry about it too much. Technically it will reduce efficiency, i don't know by how much, but it's expected to never see these fins in perfect shape. They may even purchased brand new with slight bends here and there so It's not a major concern.