Thanks for all the replies, and thanks to jdk1 for the info on sheath fit.
The 50 sheaths were ordered over a week ago and were on their way to me before I made the initial post (I called to verify this). Shipping is slower than expected (I thought I'd have them by Friday at the latest, modify them over the weekend, then ship them to Yangdu today, Monday). Tracking now says they will arrive today, so I will modify them all in time to ship to Yangdu tomorrow (Tuesday).
My tally shows 25-28 sheaths already "spoken for" (up to 32 sheaths if they fit 18" khukuris). I will send Yangdu the tally of names, actually forum IDs, of people who said they want the sheaths.
I'm thinking that sending Yangdu the money would be the best way for her to connect real names to sheath purchases. She could set them aside, with name attached, as already paid and awaiting shipment, either ASAP or with the next knife purchase. Yangdu already received payment for at least 10 sheaths.
There are about 20 sheaths still available, so let Yangdu know if you want one.
I will ask her to check the sheath fit with various sizes from her inventory, and maybe post a photo.