Depending on the size you need , a friendly plumber should have a small piece of copper pipe or a sweat fitting that you could cut a piece off . Home Depot or your local hardware store will have a brass sweat fitting you could cut a piece from for a couple of bucks .
There are also compression nuts, reducers and other brass or copper fittings that can look really sharp if a handle is made to match. Hit the plumbing section and see what tickles your fancy.
I like compression nuts personally, They thread onto the stub tenon and it you want the hex corners off, they turn with normal highspeed steels (especially tool bits ground to a narrow round point). A touch of any adhesive and they only come off when you really want them to do so.
Have also used the Oneway Threadlock ends for interchangable tools -- one handle for each size shank. Easy storage and transport.
The handles that Ken and me use have copper end caps for ferrules and they work great. The best tip I have is to turn the tenon a little big and taper it so you can drive it the ferrule on with a hammer.
We use copper because it's cheap and convenient and can be worked on the lathe with our regular tools. Any metal tube will work as a ferrule. You just want to keep the wood from splitting when driving the tool into the handle. You could use steel pipe if you wanted.
Ron,
Just saw this post. Sorry if I am too late, I will PM you anyway. I have a few ferrules from Lee Valley Tools, I can check to see the sizes, but you are welcome to them.