Most commonly called a "picnic faucet” this simple to use beer tap comes with a 6mm Barb which will ideally suit 5mm ID beer line
 
Bronco / Picnic Party Taps are an inexpensive way to pour beer and great for portable light weight systems that you can take away with you.
 
Beer Line Hack
Often these taps are used where the tap is very close to the keg itself.  If you use a really short piece of 5mm ID this often doesn't give you enough flow resistance. 
 
So a good little trick is to get some 5mm ID EVABarrier tubing and stretch the tubing and the diameter will shrink.  This will mean you still have the large diameter to join the tap and disconnect together but the middle of the beer line will have shrunk in size meaning it will give you a lot more flow resistance. You can see photos of this in the images for this product.
 
NOTE: Black disconnect and beer line is sold separately.