For me i have to apply to purchase explosives and tell the explosives branch where and when i will buy it, (which isn't handy when nobody has any in stock) and then its a face to face transaction at the RFD, if you miss the date or the dealer didn't get it in time you start over.
Nitro isn't just as hard to find but even then unless a dealer has it in stock you quite often have to book it and then wait for the dealer to get it, then apply and wait for your paperwork to come through.
Black powder is harder to get as its more difficult to transport and store so dealers are not really interested.
Its not unusual to have to plan your shooting six to twelve months ahead, it can take a long time to pull everything together especially if its something a bit different.