Zabaleta is the best bet. Normally transfer listed by City, or can get him on the cheap.
Maybe a bit overrated, but Srna is pretty much the best right back in the game, his mental and physical stats are unmatched. And you could use him as a set piece taker. He is quite expensive, but if using LFCMarshall's tactic and with your current signings, you should be able to afford him with 48 month add-ons.
You could also buy Serge Aurier and Mario Fernandes , who are young and decent and could be used as backup or straight into the first team in Fernandes' case.