Maybe if you build your own CDI, it might work better for you.
If a homemade CDI fails, at least you can see exactly which part failed and install a heavier-duty version of that part.
If they fail so soon, and so regularly, I gotta figure it is from connections going bad rather than components failing? I have over 800 miles on my cdi, and I know there are lots of people with thousands of miles on a CDI without a failure. Unless the system is modified some way or another that is stressing the CDI, you would think a stock motor wouldn't have CDI components fail so fast when they last well for others. Specially several CDI's in a row, I can understand one fluke bad unit, but not several unless there is a bad batch of CDI's out there?
My guess is if you build your own you will have no more failures. Probably not because the components are better, but because your soldering and connections will be better than what is inside the stock units. Also because you will probably mount the home made unit differently and a CDI mounted differently might absorb less vibration...
I would find it interesting to dissect one of these dead CDI's to try and see what is going on here, and just have a look inside the box for curiosity sake....