Here is the 24 Plate Ishihara, test:
http://www.dfis.ubi.pt/~hgil/P.V.2/I....TEST.Book.pdf
You might need to minimize the size of the page, but it should work. Test yourself (the 24-plate edition: seven or more errors on plates 1-15). This should give you a good gauge of where you stand. It doesn't matter if you barely see the number, as long as you can see it you should be fine. Remember that some are meant to be blank and others will show two numbers, the "right" one, and a different number that only color deficient people can see. Testing via a computer monitor at home is not ideal but in my experience, it should give you an idea of where you stand. If you're borderline, then it might prove easier in person with the real book.
If you have problems with the Ishihara plates, try the Dvorine Plates. It's easier, but that book is a bit harder to come by. Some AME's have them but you'll have to call around to be sure.
If you truly can't pass any of the alternates, then you'll have to demonstrate your ability to see the light gun signals at the airport among other things, but that's a whole other deal. It sounds like you'll pass the Ishihara's since you're only mildly deficient. Best of luck!