For your convenience, we have listed some vendors below. You may want to contact these vendors or others for price comparisons, as you are not restricted from purchasing products from other vendors. Some telephones and accessories on the recommended list are not available from Corporate Express. Below is a vendor that might carry those items. Ask for Communication products and state that you're from UW-Madison.
Headsets come in a variety of different styles.
Below are a couple of web sites that you can look at to determine what style best fits your needs. Then have your purchasing department order the equipment from one of the above suggested vendors. When ordering, provide the model number of the phone you are using.