Orchard you can try Leftfoot at Far East, Cineleisure and Cathay. There's also a shoe shop at the Meridien. But that Im not sure still there or not. Can try Denim Store at Mandarin Gallery also. Chukka is more casual, Beckman is more dressy. Moc toe esp, 875 will be the classic model.
I think you are referring to the moc toe model. of which 875 is the oro-ginal leather. the diff colour means diff model. 1907, 9075, 875 etc... all these are diff models, but same design. main diff are the type of leather used hence thats why you all see 875 in diff colour tones.
there are cheap places to get RW online from. revolveclothing and shoebuy are just 2 which i use frequently. as for how just do a quick google bah.