Zavvi UK do have the individual 3-disc Steelbook releases for the OT as being available from June onwards… so hopefully there’ll also be individual releases for the various ‘Skywalker Saga’ films available around then too…
The New Hope and Empire 4K steelbooks are sold out for preorder, though there may be more stock later in the summer.
The Return of the Jedi 4K steelbook is now available for preorder.
Update 06/04/20:
Zavvi have just sent an email notification that more than 20 previously sold out steelbook titles will be on sale again in the next few days, but only to subscribers to their Red Carpet service (£10 for one year). I suspect the ANH and ESB steelbooks might be two of the titles on offer. This is annoying but over one year the subscription might pay for itself.
Another update (sorry!):
Panic over - none of the steelbooks are Star Wars titles. Mainly Marvel.