Have a look at www.micromark.com, and search for pounce wheels. They sell a set of 3, which could be used for different spacings. As to what is right for 1/48 scale, well ... you're just going to have to experiment and see what "looks" right; it's a pretty subjective thing.
I have also seen posts in here, or maybe it was an article in FSM, where guys make their own rivet wheels out of gears they got from watch repair shops.