I have one that I got locally because they used to be over $50. in the catalogs. I remembered that Mellingers had them. Now 28.95

Here is a link that might be useful: tricolor beech/Fagus slyvactica-tricolor

You could try forestfarm. Shipping is outrageous but they have EVERYTHING at high quality. A wide selection of beeches.

There is also a place: Mountain maples.
mountainmaples.com that sells japanese maples as well as beeches. They may have the tricolor.

They have an excellent specimen of this tree at Klehm arboretum in Rockford, Illinois. It is quite a stunning tree.

I don't know where you live in Illinois, but I found some beautiful ten footers on sale at the Evanston Franks. Is there a Frank's near you? You might try there.

Not a rare item. If still looking, try searching online for Fagus sylvatica 'Purpurea Tricolor'.

I found a bunch of them at Lowes (the local home improvement box store). They often ship in trees that nobody knows about. You might check Home Depot too. They're often bargains if you're in the right zone for them.