Numrich Arms/GunParts Corp. is definitly one of the best to find some of the hardest parts to find.
I found that if it was listed as out of stock and when I went up there(I usta live like 45 mins away ) and ask Bill nicely,he would check and find one for me

But since you cant just drive up there,try Liberty Tree Collectors,Northridge,and theres a guy on gunbroker called widebuffalo-he has all kinds of oddball pistol parts.

Good luck with the hunt!!!