So far, what i've noticed is that it looks like there discontinuing all of the products except for some glow plugs and fuel, If you look on Tower Hobbies, a lot of thing say either 'limited quantities" or "Discontinued".
I'm not 100% on it but it just looks that way.
I do have to say, I have an O'Donnell Engine in my Mugen and I love it. I dont know why they just faded away but who knows...