Get the Imperial Assault Campaign module for Vassal from http://www.vassalengine.org/wiki/Module:Star_Wars:_Imperial_Assault
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There are only 8 Device tokens and 2 Recon tokens in the supply. There can be only that number of them in play at the same time.
(When a Recon or Device token is spent or otherwise discarded - for example when a crate with recon token is interacted with, or a figure with a recon token is defeated - it returns to the supply and can be reused in the same mission.)