I purchased a Rodagon 300mm enlarging lens off of ebay recently, and it didn't come with a retaining ring. I contacted HP marketing, who sells the Rodenstock lenses, and they said they sold all their remaining stock of the retaining rings to KEH when they stoped selling the 300mm. So I've called KEH, and they n longer have any of the retaining rings left. Any thoughts where I can get the retaining ring for this lens? I did a quick search of ebay and couldn't find any.