Ask someone to buy you a chess set as a Christmas gift.
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All right, how about finding a chess club in your area? You mention you used to run a chess club, is it still active? Give them a call.
Try bookshops specializing in chess, they often sell whole sets and may even have loose pieces around.
Make your own pawn out of plasticine?
Give your opponent pawn odds?
Where did your 3 yr old lose the pawn? Search your home first!

Wait! They sell individual pieces too:
http://www.chesshouse.com/Solid_Plastic_Individual_Chess_Pieces_p/e104ap.htm
Thing is, with shipping costs added on you're going to be paying close to the price of a set anyway. If you buy a second set, you'll have replacement pieces available for anything that gets lost in the future.

There are now devices available that can print 3-D objects when attached to your computer. They only sell for $1000 or so. Buy one of those, get a program to print a chess set and print out one pawn. That way you don't have to spend the $20 for a new entire chess set. Alternately, buy another chess set for the $20, save the extra set and use it for replacements since you know that you are going to be losing additional pieces as time goes on.

Do we really need an excuse to buy a new set? Time to buy up a notch, maybe get a wood set! At least, that's what I keep telling my wife, who doesn't understand why I need more than 15 sets.......
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