Levenger's often has (very expensive) rolling cart type things. Other mail order places have similar cheaper ones.There are lots of places you can get drop-lid secretary desks with sorting slots if that's your style--from mass produced in catalogs, to vintage at estate sales and second-hand shops, to fine antiques. Pottery Barn also has a lot of similar items and modular organizing items.

First decide how it will be used--standing in the entry, sitting in favorite chair, need to be in family room with folks or in the home office, will only be in one place or moved to different ones, etc. Do you want it to serve other purposes as well, such as mudroom entry storage, storing/charging electronics, or just a focused use for mail sorting.