You could call farm equipment reclaiming outlets.. (wrecking yards..)

If it makes you feel any better $100 per needle is cheap.. Try replacing needles in a Freeman 3 twine baler.. Freeman charges $ 600.00 per needle,,  The needle yoke,, I've not asked about that yet, but doubt it's any cheaper than the needles. Each knotter stack last I checked is $ 700 per stack or $1800 for the entire knotter assembly.

Ever since Allied (believe that's the company name) bought Freeman, parts have gone completely assinine !!  

No wonder the local Hay equipment builder is making 3 twine balers from 2 twine John Deere balers...... (yes it has been and is being done.)