Having a few issues with a carbon boom i have, no matter how tight i do the twist locks they seem to come lose causing the boom to shorten, is it possible to replace them?

Lee you can replace them, but the alternative is to place rubber "O" rings in the groves, this will prevent the twist lick slipping down the slots as its doing now. Take a look at my profile photo's, you will see what I did to fix mine. That was after I purchased same for my NP carbon boom. Was a better and cheaper fix, and still going strong aftet two years.
Get " rings from any hardware store, or if you see a Cat mechanic from Hastings Deering, ask him for a couple. They will have spares in their service vehicles. :-)

You'd have a van full of O-rings wouldn't you Lee?

Hey Lee surf connect sell replacement locks for the fibrespar boom. Well they used too give them a try. Cheers