Great question Kathy! Since many times the bank repossess the homes not finished, they will normally list with an agency in the local area. Some have put the homes up for auction as well. You will want to contact an agent that can pull listings off the MLS that are entered as foreclosures and then begin to work with that agent on seeing if any interest you. If you had a contract with this builder and he did not complete the contract before he went "under", you then have legal actions available and will need the services of an attorney that specializes in real estate.
Hope this helps. If you need further help, feel free to contact me at my website.
Sincerely,
Tina Evans., Broker
Luna Realty Group, Smithville Tn

Be careful on one more thing - I had one sold & the builder went under. My buyers talked to an attorney & were told that if anyone files a lien against the house down the road that they are responsible for paying off the lein.

In my area you can find them listed on the local MLS. Double check because you may have to file for permits to finish the construction. That means coming up with new plans and you will need to go through all inspections to get an occupancy permit.
Good Luck with your search.