The early tolex and thin black rexine used by WEM in the early days is no longer obtainable. However, WEM also used black basket weave tolex, the same as that used by Vox and Hiwatt. This pattern is also known as Panama. There are companies in the US that sell it but, in Europe, there are a couple of places I’ve found.
One is MAJ Electronics ( the HH specialists) –
And the other is the Tube Amp Doctor in Germany.
(Click on their names to go to their websites)
At the time of writing (Sept. 2017) both have some in stock.