I'm a NZ'er who bought a boat in the US and had it deleted from the US registry. There are two forms of evidence of deletion.
The first is simply a photocopy the original USCG "Certificate of Documentation" stamped with "DELETE" and signed by the issuing USCG documentation officer as a "true copy".
The second, which may be more useful to you is a letter, issued by the USCG, entitled "Evidence of Deletion from United States Documentation". This letter states "The records maintained by this office indicate that the vessel named above was deleted from documentation on 12 December 2007").
The USCG Documentation not only has the vessel name recorded but, amongst other things: the "hailing port" (i.e. port of registration), the "IMO or other number" (in my boat's case this was the manufacturer's hull
number) and the names of the US documented owners.
I found the USCG Documentation Center easy to deal with and if you supply them with as much info as possible that may well be able to track down your vessel in their records.
They apparently maintain files on "deleted" vessels (tho these won't show on the internet