Ideal Poultry in Texas is ships year round, but their selection is low.
being in Colorado though, it might be best for you to wait till it warms up. chicks that are shipped in cold weather have a much lower survival rate. they could get stuck in an unheated Post Office backroom over night, which would probably mean you would lose most of them. check with your local Post Office and see if they know exactly where your package will ship through and they might be able to advise you on whether it's a good idea or not.