I've found several lists of all of the dragons that are limited, but nothing where I can see what Limited dragons are currently available, and how long is left to breed them. Clicking on each dragon to find out if it is currently breedable is kind of a pain.
There are two regularly updated sources of this information:
1) Dragonvale wiki egg list. The purple colored names indicate an expired dragon, black are current: http://dragonvale.wikia.com/wiki/Eggs
2) The suggested combos at the Dragonvale Breeding Sandbox are also good source of this information:
You can also go to the combo finder and if it gives you no options to breed the dragon or no options other than two of that particular dragon then you know it's not otherwise available.
Since I couldn't find a great resource for this, and because it is a problem I've also had - I created my own. Any such resource will only be as good as the folks keeping it up to date. Hopefully this meets your needs. :)