Not sure if a YFZ rear shock will fit (I don't think it will), but others that will fit with little or no modification are the rear shocks from a 250r, 400ex, kfx400 (actually I think any rear shock off a 400 will fit), or 450r. There might be others but that's all I know of.
You can always go aftermarket and get a nice Works or Elka rear shock made specifically for your Blaster and riding style.
'02 Yamaha Blaster - '03 Front Hydraulic Disc Brakes, Elkas on the Front, +3+1 ASR a-arms, DG Bumper, PB Phantom Exhaust w/Spark Arrestor Kit from ALBA, Renthal Bars, Premix, No Air Box Lid, Uni Air Filter, UM Swinger Skidplate, AC Nerf Bars, Holeshots all around