I had the same issue looking for a mount I got fed up looking and just ordered a "RC Plane Airplane Metal CNC L Motor Engine Mount" from gemstraveller on ebay. I figured at $4.80ish I wouldn't have been very mad if I couldn't get it to work unlike most of the other mounts I've seen for $10-20 and had no idea how I would go about mounting it
the holes to mount it to the chassis were a little small for the screws I used so I enlarged them with my one drill bit
And for the motor I had to royally enlarge the hole on it. Grinding the hole out to fit the shaft through actually was the part that took me the longest. I probably spent a hour on the mount alone everything else was around 30-40 mins tops.

Too bad the pic of the bottom is too blurry or you could have seen the horrendous job I did measuring the holes locations and how I was off by 2-3mm on each one.

Here are two of the pics I took of the mount (rest were too blurry) before the cameras battery died.