Hey Dusty,
That's a good looking bass!
I think you might have to go the custom string route.
Quite a few manuacturers make short (30") scale string sets to conteract any loss in tension, however they all seem to be 4 string sets and in roundwound only, from what I've seen anyway.
I've got a 33" bass and I've been in touch with Malcom at Newtone strings, (
http://www.dwmee.34sp.com/ - odd website name, I know) I'm afraid he's UK based, and he's happy to make up custom sets for any scale length. He might be happy to ship to you.
I used to use his strings a few years back and they where great.
Back then it was about £30 per set, that was for a custom guage 6 string set.
With regards to flatwounds, I'm not sure if he does them, on his site it says that they're not available at the moment.
Hope that's of some use mate!
Looking forward to seeing how it turns out!
Eude