3 relievers to target via trade - 1. Brooks Raley
For multiple reasons, Brooks Raley tops the list as a reliever the Cubs can target in late-game situations. For one, the Cubs critically need another productive lefty in the bullpen. For two, if he doesn't work out, he has a club option after this season, so you could always keep him for another year after this. For three, he's been lights out this season for the New York Mets, who surprisingly find themselves 18.5 back in the NL East at the time of writing.
On the season, Raley owns a sparkly 2.08 ERA with 34.2 IP this season. The Cubs certainly need to bolster the back end of their bullpen. The only hiccup here is that the Mets may want to avoid trading Raley, given that he's been solid and has the extra year of control, so they can begin to retool for 2024. However, given the state of their farm system, particularly among pitchers, and how awry things get at the major league level as soon as someone has to miss time, the Mets need to find a way to rebuild as much as possible. With their unlimited funds from owner Steve Cohen, the Mets will have no problem finding another relief arm or two in free agency for 2024.