Are you required to have transactional activity of customer with Bank you are requesting information from?
Example: Did 314-B with one bank(a) for source of funds. They replied their source of funds came in form of external transfers from another bank(b). Our bank(c) has not had any activity presented by our customer from bank(b). I would like to request source of funds from bank(b)on our customer.

No.

FinCEN's guidance on marijuana related businesses contains a specific suggestion that if you closed an account based on what you thought was illegal activity you should contact the bank to which the customer moved his business under 314(b).