I needed a shifter for my R151F and couldn't find one either. Marlin's shop told me R150F and flip the base backwards so thats what I did. Been running it a few years. I "MAY" have had to mod the bolt holes? I don't remember. It wasn't too hard to do. I have pics. PM me.
Not sure of your message . Did you want me to try and find you a base? Is marlin confurring that a G52 works? I have that right now on my R151 and it works. I wanted to keep my G52 style boot and the new seat I just put in the shifter base.