If you have been dealing with a dealer who has gone bankrupt you will need to contact his or her trustee in bankruptcy. Your claim will rank behind that of any secured creditors and preferred creditors, such as HM Revenues and Customs, and employees.

You should not assume, in the absence of a clearly written agreement between yourself and the gallery, that title to ownership of your work only passes when you, the artist, are paid.  You may well find that your work has been sold to an innocent purchaser who will have title to your artwork, i.e. will legally own it, leaving you to pursue the gallery / dealer for the unpaid monies due to you as the artist.  You will not have a claim against the purchaser for the return of the artwork.

If the gallery is a company you will need to contact the liquidator or receiver: if the company is in the UK, you can find out who has been appointed by making a search with Companies House.