I too, own a Horizon 39 and have been researching' with little in the way of results, for the past six months.
I started with the HXY prefix on the hull number. The HXY (MIC Manufacturer Identification Code) now belongs to HOLBY MARINE of Bristol, RI. All I could get from the USCG MIC Site was that Holby "has been using this MIC since the late1980's." I contacted Holby (A Mr. Barrett) who had "no idea what I was talking about."
There was an owners group run by a guy named Bob Mahafy in Virginia. I contacted him by e-mail. He informed me that the hulls were made by Columbia!(?) Subsequent contact with him proved fruitless and ended when he allowed as how he sold his Horizon and was no longer associated with the group. My impression was that he no longer wished to be bothered with it.
I tried to get info on Barry Scharf and found no recent listing in Clearwater but found one in Treasure Island. Will wait to see what that turns up.
The hull design looks like a Shannon and while an e-mail to Shannon produced no hard information, there was considerable interest and a promise from Shannon's CEO to pass my request on to one of his employees who might know something about it. That was the end of that.
In Johnsboatstuff.com there is mention of the Horizon in a reprint of a "Cruising World" article which talks about using "fuzzy Logic" in choosing a cruising sailboat. On that list, it shows the Horizon 39 in the "$75,000 to $100,000" list of BEST CRUISERS UNDER $100,000 - right up there with the BCC's, Hans Christian, 38's, Pacific Seacraft 31's, Cape Dory 36's, PC 34's and Morris 28's!!! A nice group to be in.
Bottom line: I guess we have to remember the market turbulence in the 80's for "yachts." Information comes in dribs and drabs. I will continue my search and "thread in" if I come up with anything further.