So you're a Do-It-Yourselfer.  You clean your own harmonica.  You are confident about disassembling and reassembling.  You can do all of the maintenance except, you can't replace reeds.  Here's the solution for you...

You disassemble your own harmonica and ship me only the reed plate that needs a reed.  You tell me...

• the harmonica's make and model
• the hole number
• blow or draw
• pitch name (i.e.: G or C or Bb)

• If you have a custom tuned harmonica, you should tell me the pitch and the specific octave C4, G6, 
• I will tune the reed to match either one octave up or down, unless otherwise requested.