They can be downloaded here.
The way to use them is quite straightforward.
1. In secret work our your army list.
2. Select a substitute vehicle (and make a note against the army list).
3. When first placing the vehicle(s) down on the table-top, use the substitute(s) rather then the one you have paid for on the army list. Only swap the modes over when the enemy correctly identify them.
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Here is a picture from a game I played last night at the Harrogate Wargames Club. It's early on as my vehicles enter the table. Substituting vehicles, the King Tiger and Jadgtigers are representing Sd kfz 251/22 with Pak 40s, The PIV is actually a Hummel and the Brummbar is playing as itself, after it has just been identified by the enemy (after a lucky combination of die rolls forced a Churchill crew to abandon their tank :) )
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