Hi Nechesh,
I must say your friend's effort is commendable. Even in Malaysia, where the indigenous sarung forms are slightly different from Javanese ones, I have encountered a few improvised sandang walikat style warangka like yours, made by craftsmen from Kelantan and Terengganu unfamiliar with the style.
The other option would have been to refit the blade into an existing sarung, though the mouth might need to be enlarged or modified etc, not an option preferred by some people.
One thing that has worked for me though was to either give the craftsman an original sarung to be copied, or at least schematic drawings with correct measurements for the piece. I can also understand that sourcing the right kind of wood is also problematic (it is the same case here, kemuning is becoming a bit rare these days, though sena wood is somewhat plentiful, if you're willing to chop down trees planted by the municipal authorities
).
Have you ever thought of exploring the mail order option i.e getting an Balinese craftsman to work on it based on an outline drawing of your keris blade?