I picked up this lens for a really cheap price during my visit in Vietnam, those who own it has very good review of it. One fine day I was itchy find a tripod collar for it, only to find on several forum that the original Olympus tripod collar has been discontinued and very difficult to find.
So I did some research and found the next similar replacement:
There are certain ‘high quality’ tripod collar out there do more than just holding the lens, it has a little track thing that allows the designed lens to slide in and rotate without dropping out. I wanted to find a collar that is similar in diameter yet has the track to do so.
The closest I found is a 2nd collar I imported from China originally for Sigma 150-600mm. Unfortunately the diameter was about 1~2mm off, and fortunately the difference gave me a leeway to design a 3D printed adaptor.
The end result works 90%, the first print is too thin (too loose) and the second print is too thick (too much friction for rotation). I could have perfect the design with another print, but with this I am already very happy with the end result.
Witono's Freestyle 
Are you posting your models somewhere?
Would like to include them in my collections of Olympus parts, more here: https://www.printables.com/social/6672-steve/collections/126037
I did a tripod collar for my 35-100, and it took WAY TOO many iterations.
In the end the lens was too heavy my me, and I just sold it.
Best,
Steve