My capacitor is not available anywhere, but there are close ones
Those capacitors will usually have a tolerance of anywhere from 5% to 20%.  The exact value isn't critical.  The motor may turn a tad faster or slower on a given setting, but it won't do anything disastrous.
The part you gave as an example (5uF + 6.5uF + 6.5uF) shouldn't catch fire or shorten the life of the fan.

Make sure that you get a part with the same or higher voltage rating.  A low voltage part will come undone if used outside its ratings.
Make sure you buy a quality part. Cheap parts may be just cheap and blow up on you.  They might also be marked for a higher voltage than they can really handle - buyer beware when buying cheap replacement parts.
Be careful when you install it.  If you do it wrong, you could cause a short circuit that will kill your fan when you turn it on.