If this is an art project or something similar (please post the results!) you should go to the grubbiest 2nd-hand store in town and ask what they have in the dirty back corner. Around here (US), I could probably get a dozen keyboards at every 3rd or 4th thrift store for $1-$2 each which translates to a penny or 2 per cap.
But it would take a few hours of driving around, at least.