You'll find some listings on Google. Search "dfs loudspeaker". I think they're out of business.
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You are thinking of "upgrading" what is essentially an old cabinet? Seems like a bad idea to me because you won't find the same drivers and won't get good results by sticking any drivers you do find. What will you do about the cross-overs? You are basically setting out to design a loudspeaker, but with the extra burden that it must be around this particular cabinet!
Do you realize that very successful speaker lines had to be redesigned or shut down when the drivers became unavailable?
I would seriously think about just buying a working pair, new or used.