Luis,
I recently had the same issue but did not have the luxury of time.
Ring gears are available in Europe.
I found some but could not wait to get one.
Google is your friend.
They may have been on Ebay Germany or UK.
And yes new flywheels come with a ring gear unless someone swiped it.
You could go on MyE28.com and post a wtb for a flywheel and more than likely find a good used one. The tricky part is finding one with the "ball" imbedded in it like original. Others work you just have to find the TDC mark and put some white paint on it. This is what I did because my 3.5 was a Motronic motor with pick-ups at the flywheel.
HTH.
Gary