This rather depends on what sort of limit switches you want but if you want professional grade equipment rather than no-name Chinesium then I'd go to RS. Although they are first and foremost a trade supplier they handle personal accounts too, and cash sales can be done via the website. Support is very good and as far as switches go, they have enough to sink the titanic. They do their own lines of cables, switches under the RS Pro line, and they are effective and well priced.
Farnell are also very good and sometimes cheaper - Best to check both.
Amazon sometimes do well but don't expect any kind of support, they're ok if you want basic stuff down to a price but I'd rather go somewhere that i can find the same thing a year later if I need to replace anything.