150-600mm at Amazon US&CA&EU, BHphoto, Adorama, Om Digital, FotoErhardt, Calumet, WexUK. OM Germany, OM UK, OM, Italy, OM France.
On PetaPixel they write:
There is no denying that the 150-600mm is versatile and make no mistake, it’s still fairly easy to carry around all day. But when the higher price tag of $2,700 is added to the OM System version of the lens, I can’t help but feel that I want more light or less bulk for my money. Still, if you need a lens that has humongous telephoto reach the OM System 150-600mm is worth a look.
Frankly, there aren’t many practical choices to consider which is why this lens will find its way into many users’ bags. The Pro series OM System 150-400mm f/4.5 gives more light and with its built-in teleconverter also competes for range, but the professional pricing is prohibitive to almost everyone.
There may not be any alternatives but with the compromises of using a full-frame formula aside, the 150-600mm is still functional and the images are beautiful.