How many do you need?
Anyway, the venom cannon feeder arm is a good idea, but if you need more, you could try some other weapons. The BS feeder arm would work as well. Basicly what you need to do is to put a little glob of GS on the end of the arm. Get a couple pieces of wire and bend them up and put them in the GS to make lashes. Then later you can coat them with a think film of GS and put a hook on the end. Where the GS connects to the arm, if you aren't a good sculptor you can use an extended carapace piece to cover over the transition. This can work with any warrior sized tyranid arm.
Another trick is to only give one lash per warrior and have the other arm be a scything talon or something. That way for each 'pair' of lashes, you only need 1. This should be legal because this way of doing it was featured in the old dex and had some pics in other places of the model.