Check with your bank to see if they have an international teller. Mine (Wells Fargo) has an exchange service which will exchange as much as you want at the established exchange rate and better than what you'd pay for one on eBay. I have a few of the Darwin notes myself that I didn't change back. Also I have some Falklands pound notes that I found out the hard way can't be exchanged anywhere but the islands and an office in London. Wells Fargo carries Euros, Canadian Dollars, GB Pounds, and Mexican Pesos at all time. If you need another currency, they'll order it for you free of charge.
As for the coins, you'll have to get them online. Banks only deal with foreign banknotes, not coins.