Hey, my RG40 came without the cylinder release as well...
Who is taking all the RG .38spl revolvers and fiendishly removing the cylinder release? Its just cruel I tells ya!
FYI, You can pull forward on the ejector rod to release the cylinder untill you do manage to find a replacement. I fabricated a few replacement cylinder release buttons myself by hand, including a really nice aluminum one, but now the hole on the cylinder retaining pin they are supposed to screw into is stripped out, so I'll have to order a new one of those before I can have a cylinder release again. Oh well, such is the curse of working with an RG revolver!