G'Day,
I had a similar dilemma as you. I also had quite a bit of leather lying around and ended up making my own. I include a few pictures of the various ones I made. I started with a size similar to the Micra, but that was a too tight fit. I have an original Micra sheath and the Squirt fits in there but one can see the stitching taking a bit of strain. It needs to be a little bigger.
Two things that you should take note:
The Squirt is slightly thicker than the Micra (which was my starting point) add some additional leather if you do a pancake sheath.
Add additional leather on the closing loop to accommodate the folding/pulling of the leather around the belt clip.
Cheers,
Pete