Well, usually if you want to have internal and external sales built into one system it would be a custom development. Not sure of what your budget is, but if it is very small like most companies these days, you can look into OSCommerce. It is an open source web order and backend management software. Tons of developers out there that can set it up (including myself) and it is very user friendly to manage for online sales. I have never had to integrate it into a brick and mortar however so i am unsure of how possible that is.
this link contains some different software packages that may cover what you are looking for: http://multichannelmerchant.com/opsandfulfillment/ordermanagement/systems_solutions_2/
Or you can just google something like Multi channel order management