AIWB Holsters I Use.
For my 642, I use a Blade-Tech "Klipt":
Klipt J Frame Revolver Holster | Blade-Tech Industries
For my 640Pro, I just bought a Galco "Stow-N-Go":
STOW-N-GO INSIDE THE PANT HOLSTER: Appendix Carry Holsters | Galco Gunleather
Unfortunately, the 640Pro did not fit into the Blade-Tech "Klipt" which caused me to buy the Galco.