Don't worry about this one. It will come in time - latest once you have your third weapon through story progression. The fast one with the long range. When you have the next bunch of small enemies like bugs, just keep on mashing X. Your combo will not break if you get hurt, only if you are knocked down. At one point I got a 307 hit combo.
One more thing: I suggest you break your combos once you have 100 hits. You will get massive upgrade point bonus until 100 hits, but once you have 100 the next bonus is by 200 hits - you will get much more starting a fresh combo.