PLT OF SMA ACFT HAD A NMAC WITH AN ACFT TOWING A GLIDER OVER A NON CTLED ARPT.

Narrative

I WAS ON A FOREST SVC FLT APCHING MINDEN ARPT FROM THE SE FOR LNDG. CALLED UNICOM FOR ADVISORIES APPROX 7 MI SE. ADVISED MY POS AND ALT AT THAT TIME. A GLIDER TOW PLT SAID HE WAS DEPARTING RWY 30 AND ASKED WHAT RWY WAS GENERALLY IN USE AND HE SAID RWY 34. I ADVISED HIM I WOULD BE MAKING LEFT TFC FOR RWY 34. I ANNOUNCED MY POS AGAIN APPROX 2 MI SE OF FIELD AND INTENTIONS FOR L TFC FOR RWY 34. AT NO TIME HAS THIS TOW PLT ADVISED ANYONE OF ANYTHING (NO POS; INTENTIONS; ETC.). I ANNOUNCED MY POS OVERHEAD THE ARPT ON A L XWIND FOR RWY 34. SEVERAL SECONDS LATER; THE TOW PLANE AND GLIDER PASSED APPROX 10 FT BELOW US IN A NW SE DIRECTION. IN SPITE OF THE FACT THAT MYSELF AND 2 FOREST SVC PAX WERE CONSTANTLY LOOKING FOR THE POSSIBILITY THAT THIS TFC WAS STILL IN THE ATA; WE AT NO TIME SAW HIM AFTER HIS DEP FROM THE RWY 30. HE; IN SPITE OF MY CONSTANT POS RPTS AND RPTS OF INTENTIONS NEVER ONCE ANNOUNCED HIS INTENTIONS TO ANYONE. I WOULD HAVE THOUGHT HE WOULD NOT HAVE ELECTED TO CIRCLE BACK TO AND OVER THE ARPT; KNOWING I WAS INBOUND FOR OVERHEAD APCH TO RWY 34. I CAN'T EXPLAIN WHY WE COULD NOT SEE HIM; EVEN THOUGH WE WERE INTENTLY LOOKING. (THE FACT THAT HE WAS BELOW US WITH GND CLUTTER BACKGND DID NOT HELP!) (WE ALSO HAD OUR LNDG LIGHTS AND STROBES/BEACONS ON.)