Sure can! Knit Picks
, and Denise
are four different brands that I can think of off the top of my head that have what's called interchangeable circular needle sets. They come with different sized needle tips and different lengths of cables that you put together to make whatever size/length needles you need.
I love circulars. I just started making a scarf on size 8 straights (all my size 8 circulars are holding other things) and it's driving me nuts. I keep hitting my thighs or if my kids are trying to snuggle with me, I smack 'em in the forehead with the ends of the needles.