Hi,
Black and Blue is an exceptionally difficult plant to get seed from. Either there is no seed set or the seeds drop out immediately when ripe. This makes sense though because this type of salvia makes tuberous roots. Plants that do that often are less generous with seeds.
There are a few things you can do though.
One if you've got a good local family owned type nursery that carries Proven Winners annuals, you can ask that they order it for you in the spring.
Another is to trade on the Plant Exchange Forum in the spring. People who live down south will have nice sized starts if you have plants to offer in exchange.
Lastly, try planting your plants on the south side of your home close to the foundation. I did this a couple years ago with mine and it has come back for me. I originally did this because I figured what the heck either throw it out, or see if it lives. Last year, it grew, but did not bloom(thought it did in the first year in the pot of course.) This year, it has been blooming for a few weeks now and looks great!
Hope this helps,
Remy

So then what I am gathering from this is unless you have a tarp around the bases of your B&Bs you'll be hard pressed to get any seeds when they are ready.

So then, is there a way to determine how long it takes for the seed to ripen prior to the flower drop off?

Hi Dakster,
I'm not sure about the time. I've never bothered trying since I've read so much about how hard it is to get seed. But when I collect seed from my Salvia patens 'Cambridge Blue' which also likes to drop seed quickly when ripe(but it at least makes seed quite readily,) I go out there checking every day. You can see down into the calyx that seeds are developing.
Remy