Long story short, i found gravity gun in infinite mode and gave it in kerfur-o hands. After some time the game saved. I KNEW that every item in kerfur's hands disappears after save load, but when i realised it was already too late. I've tried to use multiple save editors. Some of them were just money cheats for kids, other variants didn't want to work with UE saves. It's a huge pity for me that i lost this very special item and i want it back. Any ideas how to bring it back guys?

I did it. So, all you have to do is to go in sandbox mode, spawn an item, then save and quit. After that you have to rename sandbox savefile's name first letter according to first letter of your save file where you want to see that item, make them the same savetype (for example b_(yourfilename) into s_(yourfilename)). After that just return into your edited sandbox savefile, place your item into mailbox, save, and take it from mailbox in a savefile you wanted to transfer your item in. Profit!