If you are a Realtor representing the lender, you will need do do a lot of the work yourself or have your own team put together. Many lenders have you do the work and reimburse you and not too fast at that.
This is to the extent as to show the home, that is why you will see the foreclosures in different such different states of repair. Different lenders will allow for different work done and different Realtors do a better job of preparing the house.
Now if you are a Realtor representing the buyer, who does the work has to do with how the buyer is going to pay. Is this work done before closing or does the buyer have an FHA203 loan. The buyer may choose his/her self a friend or neighbor if he is paying but if in loan it must be a someone certified to do this type of work and in business doing this type of work.
Your question is not real clear so I hope this helps.
If you are representing the lender and need contacts - contact some Realtors that you see have a lot of REO listings.
Most lenders don't seem to want to do repairs.
Are you representing a buyer or seller.
If you need board up, clean up, yard services, etc there are some companies around that will do this.
Just do a google search with your zip code and REO services.
You may want to look into FHA 203(k) loans. I don't do them but maybe I could refer you to someone.