So they are already out of stock?

They are still in stock now.

Is DFROBOT still running the Monthly Raspberry Pi Day from 8th to 10th of each month, which during this period one is able to enjoy a special offer to get one and only one piece of Pi 3+ for just ＄29.95?

Because Rpi 3B is out of stock now, we will resume the special offer, the same is model B+, we will provide a new special order for this product.

Can I pay for the B+ special offer now and have it shipped when it's ready? I can wait, I just wanted to get the Monthly Raspberry Pi Day deal.

You still need to wait till the period of deal when it is released.