The size of the barrel adjuster is M5, you should be able to get some steel ones from a good LBS. Original ones are made of brass or some other soft material, it's probably not stuck there too bad so try pushing a screw driver (I'd use phillips head, but grab the one that's nearest) into the broken one (with some pressure) and screw it out.
I wouldn't bother replacing them with original ones because this may well happen again with them.
The size of the barrel adjuster is M5, you should be able to get some steel ones from a good LBS. Original ones are made of brass or some other soft material, it's probably not stuck there too bad so try pushing a screw driver (I'd use phillips head, but grab the one that's nearest) into the broken one (with some pressure) and screw it out.
I wouldn't bother replacing them with original ones because this may well happen again with them.