Prob'ly more than you'd first think . The mass of ships taking stuff from the US had to return for the next load , so cargo space was abundant on the return trip. Springfield overhauled thousands of small arms of all types in those years , Duff's red book has the exact figures , I believe. RIA would have been similar . Many were sent back over and used , with many being lost or re-rebuilt after the war , which would erase the RIA markings. Numbers done and numbers remaining are two different things.
I answered the way I did because I have a RIA / FK marked rebuilt carbine , so I was sidetracked.
The remaining examples tend to be hard to find.
Chris