Is there a posted schedule of when some black lion items might come back?

I would like to get Lord Caudecus's pistol skin, which isn't in the market anymore. Is there any place that shows the cycle these things go through, or are they "miss them and they are gone?"

There's no posted schedule, but most things do cycle back through the gem store from time to time. Keep an eye on the Gemstore Items: New/Returned/Sales thread for updates.

Let's say that every item will be avaible 2 times per year. Check wiki for specific items information.