Spurs have good full backs in my opinion.
Bale is probably the best/one of the best left backs in the game, and Kyle Walker does a great job at right back.
Covering these two are Assou-Ekotto and Alan Hutton/Corluka. At least thats how I do it. There are players with better stats than Walker but I favour the English players every time.
If you are set on replacements/back up, I got Kolarov for cheap (transfer listed) and he did a good job while bale was injured. Theres also Coentrao.
Right backs include players like Santon and Renan.