Take a look at Forestfarm.

The main problem with grafted combinations is the H. virginiana stock never gives up trying to take over.

What I heard (a number of years ago) from a nursery grower who is experienced in growing Hamamelis is that they are difficult to root (low success rate), except for the straight vernalis varieties. The same grower claimed that if suckers are removed promptly when plants are young, suckering generally becomes less problematic as the plants get older. He also noted that suckering on grafted varieties is usually worse if vernalis is used as the root stock rather than virginiana.

I assume that Forestfarm's Hamamelis are all grafted.

On mine ('Jelena', 'Rubin', and one other I can't remember) the suckering stopped after about 5 years. Or at least slowed down. It's nothing like, for example, the disastrous suckering problem I've had on my Prunus mume 'Peggy Clarke'.

It has been my experience that named Japanese apricot selections, including 'Peggy Clarke' produced by the LE Cooke Co come on a plum rootstock that replaces the scion after the latter reaches some size, say 10 ft. across. Surely this is a (somewhat briefly) delayed graft incompatibility issue, that could be resolved by using a different rootstock. I used to have 'Matsubara Red' and 'Peggy Clarke' here, as well as a 'Peggy Clarke' at a friend's Island County place - all are gone now. The third example grew like a weed and flowering sensationally for a few years, also fruited heavily at least once. Then the top rapidly dwindled away, to be replaced by a forest of vigorous sprouts from the rootstock. Which also sent out nuisance runners that will need to be grubbed out, if that part of the garden is not to become a thicket of them.

Mine came from either One Green World or Raintree - I am pretty sure it was the latter but I tend to confuse those similar nurseries and what I've bought from which one.

If it's grafted and of typical garden center size and shape - as in head high, with a clear stem and elevated crown - then it might have been grown by Cooke. Unless neither retailer ever buys from them.

"of typical garden center size and shape"

I wouldn't say so. It was a pretty typical mail-order "one whip fruit tree". It grew very fast at first, it wasn't until the 3rd or 4th year that the rootstock went berserk.

Agreed. Another case of buying a time bomb.

Own root witch hazels... do they exist?

Sure and here's a perfect example. H. vernalis outside the dining hall @ Swarthmore College this morning. This massive plant can be spotted and smelled a mile away.

Jon Genereaux was growing them in a nearing frame a few years ago at Hidden Lake.

Klehm's sells quite a few H vernalis cultivars grown on their own roots. Here is a link.