Don't tell anyone.
If they don't have the Federal license to sell it they are breaking the law.
This has been covered before but a club or any group of friends can appoint someone to be their "agent".
The "agent" collects the orders and payment from all of the people who want black powder keeping a written record of who wants what and of their payment.
He/she then orders and pays for the powder, its shipping and the Hazardous Material fee specifying that it is to be delivered to his/her address.
When the powder arrives, he/she must contact the others and tell them to come and get their powder which he/she then gives them.
This is totally legal as long as the order doesn't exceed the Federal allowance for an individual purchase.
The catch is, after the powder is delivered, if the agent or anyone else actually sells their powder to someone else, that is a sale and the licensing requirements apply.