iMac Mid 2010 USB recovery I replaced tha hard drive on my Mid-2010 iMac because it failed and was unrecoverable.

Now I need to install Mac Os High Sierra (the latest for Mid 2010), using a USB drive I have to create on Windows, because I have no other Macs.

Now, I know I can use TransMac, but the problem is that I can't find any install DMG online. I also tried to search for Sierra instead of High Sierra, but I couldn't find nothing.

I can't download Sierra from Mac App Store, because I'd need a Mac I don't have right now. 

So the main question is: where can I find the DMG file I can use to create the USB recovery drive with TransMac?

Thank you and sorry for bad english!
If you kept the firmware on your Mac up-to-date, you can use Internet MacOS Recovery. The mid 2010 iMac didn’t ship with that capability, but it was added in a later EFI update. If so, then just make sure it has a decent Internet connection and hold down Option-Command-R at startup.