sounds like you have the ;standard auto', an 'RST-4' depending on what frame is currently on the gun, ( yes , I know it SHOULD be an 'A-54' frame but they have been swapped around over the years, so gotta KNOW just which one is on your gun)....if the bottom grip screw panel on the left side is LOWER than the one on the 'right' side, you have the older, original style frame on your gun........re: A-54 get /find panels that are proper ,correct for your gun, I know there have been some wooden ones floating around e-bay and other places for some time, that were a very GOOD deal, black eagle medallion on the left panel ,checkered walnut and they were well UNDER $15-20 a set, thats a GOOD deal..if you want the original ,hard rubber ones, then you may have to shop around, I sold my last pair a week agop to another Forum member,can look for MORE if you really need or want that type ( original to your gun)
as for the magazine any of the older, chrome bottom ones should work, your gun came with a single slot mag, later, for the A-100 they became two slots ( both sides) and as you note,the button would have to be reversed to fit YOUR gun, no big deal, easy enough to do...in fact even any of the newer ,later MK II mags can be made to work in your gun also........they too need to have the button reversed,though, they are done in a different manner, the plastic bottom has to be removed and the spring lowered to free up the follower button..........
good luck ..................