The plate is a Spoke Protector and it is purpose it protect te spokes/wheel from damage should the rear derailleur (RD) become misaligned. the protector (aka dork disc) keeps the RD from getting jammed in the spokes.
As for the front wheel... the odds of finding an exact match are slim but I suspect that something very similar can be found rather easily at your local bikes shop (LBS) or CO-OP
Sorry yo hear of your loss
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk