The office spaces and warehouses may not be so bad, because you have a fairly blank slate that you can build and customize the way you like. Plus they are probably already zoned for commercial use.
If you tell a real estate agent what you're looking for they can do a lot of the house hunting for you. Sometimes they get leads on properties that might become available before they actually hit the market. Another idea is to pick an area that you like and simply walk or drive around looking for buildings with For Sale/Rent signs. This takes a lot more of your time, but it also gets you in touch with the area that you want. You could also ask banks if they have a list of foreclosed properties, although your real estate agent may already have this.