Understand all the excitement and the need to get the ducklings the day before yesterday, i hate to be the party buster but:
- You have made all you preparations?
- Brooder is ready with a heat source, food and water?
- Somebody can have an eye on them when you're not there?
- They have a safe place outside once they have outgrown their brooder?
- …
- That gender question: Even if you could perform vent sexing, the store personnel would (should!) not let you hold the duckling. As far as i know farm stores all sell straight run ducklings, so there's a good chance you will end up with too many drakes. - Not fun!
- Breeds: My first ducks were Fawn and White Indian Runners and i still like them best. Somewhat skiddish, but that has changed this spring. They are just fun to watch, bowling pins on legs with brown vests and white boxer-shorts.

With this years Spring Ducklings i got Magpies, Buff Orpingtons and White Layers.
The Buff's are really calm and friendly and my little drake "Erpelchen" is a cutie-pie, always around me and asking for some duck-crack (meal-worms). I can pet the Buffies while i feed treats to the ducks.
The Magpies are wonderfully feathered, really deep black with blue/green shimmering stripes at their wing-tips. But they are a bit skiddish and don't like to be touched and they are a bit boring, not running around so much as the other ducks do.
The White Layers look like "Honey i shrunk the Pekin ducks!" fluffy white slippers on legs. They are cheeky, loud and just funny. Always in competition with the grown-up Runners for food, water, the pool and exactly that particular spot in the sun. 
I would never again buy ducklings from a farm store again, i bought my first ducks (the Runners) in the local Rural King last year. But at that time i did not had an eye for ducklings and their needs. In the mean-time i have seen too many sad things in many farm stores: Ducklings shivering and piling up in one corner of the stock tank because the heat lamp burned out, drowned ducklings, trampled ducklings, Ammonia ducklings and most of the store personnel has no clue about care and is not interested in the health of the little birds. They are just a commodity in the store that must be sold before the expiration date.
I can only recommend to mail-order ducklings at a large, established hatchery. My Buffs and Maggies came from IdealPoultry in Texas and the While Layers are from Metzer Farms in California. Shipping through USPS is relatively safe and fast and you can order exactly what you want, breed and gender. I was a bit unlucky with one White Layer, but the majority of mail-order chicks arrives unharmed.
Another possibility to obtain your ducklings would be a local breeder in your area - you can look out in the
Colorado thread here on BYC. I am not sure if there are any poultry hatcheries in Colorado after "Larry's Poultry Hatchery" has closed. So far i've only found chicken hatcheries around Denver…
Ok, 'nuff serious thoughts, here are some ducklings.
A cheeky Magpie:
Three drunken ducklings at the bar:
And the king of the castle:
Have FUN with your ducklings!