I want to offer a fairly consistent single-origin products to my customers. In general, which beans do you tend to have a consistent supply of, and which ones are more seasonal or variable?
There is no really great answer here.  Which is one of the reasons, I, as Chocolate Alchemy, am here.  Very generally speaking, most everything I carry I attempt to keep a steady supply of, and unless otherwise stated, it's here for a pretty long haul.  And when it's not here long term, I say so.  For instance, everything I currently have is 'long term' with the exception of the Venezuelan.  It's not always around mostly due to the difficulties of working in origin.

As for a more useful answer, I like to work hand in hand with both my suppliers and my customers, keeping everyone in the loop as to what I need, what I have and what I can offer.  But I can only do that if you too tell me what you need (like the above question).  I put out a monthly wholesale e-mail that lists what is available, how much is around, for how long and also what is up and coming so you can attempt to plan accordingly.

So, if I don't say otherwise, bean supplies are stable and readily available.  If you want to be really sure, write and ask me and I am more than happy to work with you to make sure you have what you need - that's my job and what I love doing.  If a bean is in limited supply, I will say so, and basically all bets are off how long it will last.

I hope that helps.