Hi Frob,
No, as far as I know, no one here has built a small-diagphragme mic yet. i know that Tim C. is thinking about trying...
To find a place to buy a SD capsule is not difficult - think of the exchangable CK-series SD capsules for the AKG C451 system e.g.
These can be found second-hand at reasonable prices.
Or the recent Oktava with interchangable capsules - those are still in production, I think - try your local Oktava pusher...
Jakob E.