Hi Matt, if there are ongoing supply problems then JL will often mark products as no longer available because they don't have reliable information to advise otherwise. It isn't unusual for these items to reappear at a later date without notice though.
My instinct with the Haegan range is that it will not be restocked since much of the collection has been depleted for a considerable time. It is worth checking the site now and again however, just in case.
With regards to the similar products you mention, I am not aware of these but it is highly unlikely they are the same product for the simple reason that if there was stock available John Lewis would have it.
I would also be careful trying to match existing furniture with what appears to be a near enough alternative since products with a natural woodgrain finish can look altogether different when placed next to each other. Even items from the same range can have significant differences in shade if there has been a long time gap between manufacture.
Sorry I can't be of further help, this an issue with a lot of furniture range at the moment and we can only hope it gets better in the new year.