man I feeel you. by that point my villagers sent over my mail more statues than reddd. haha I think statues are kind of rare, all you can do is keep tt-ing back and forth. it will happen eventually. I did the same to fill my galery and trade stuff, and now it's completed, but I legit tell you that there were a few statues that I traded for that I never organically saw in my redd ship honestly. so bad luck really is a thing.
tt-ing back and fort for redd is very tiring. so I recommend you to do it in sessions. Like lets say you did it for 1-2 h today, and have 1/3 of the gallery filled, take a break and go back to playing normally, and when redd shows up naturally again, do the back and fort again. it won't feel that grindy anymore. thats what I did at least!
good luck!