I used to work as a bank teller about 7 years ago. $3500 is pretty low for a bank to be carrying. If you gave them a days' notice they could probably get you almost a hundred grand.
Of course, a lot might have changed in the last seven years, but when I was working, $3500 would be easily available.
The best gag is that one has to pay to withdraw larger sums of money, it's like paying if you want to take something from your fridge.
One night I dreamed of chewing up my debetcard - there simply is nothing like hard cash in your pocket!
Its not your money, or anything, why should they keep it on hand? But don't worry, the Fed should be helicoptering some your way shortly.
What really worries me about this policy is that by having to withdraw $3500 cash multiple times, the anti-money-laundering authorities might assume you're trying to dodge the $5000 limit (is that the correct number) that once exceeded, requires you to file a form explaining why you want so much cash.
I hope this policy doesn't cause you much trouble. Perhaps it might be better to order online, where debit/credit cards are the norm. In fact, if your broker requires cash, perhaps he's trying to hide something from the authorities. That's highly improbable, but it may be a valid concern.
Stay safe. There's no point in having stable money if you're too busy locked in a cage to enjoy it.