And for even more inspiration, I've been trying to find someone who might sell a narrow and light beadlocked alloy rim for use with a 10" (max) wide tyre.
It's not easy to find.
I've considered going to speedway wide 5 - 10.25" PCD, with an adapter, but I can't get them off the shelf at under 15X8, and custom adapters would be required.
Everything else just comes back to truck rims or circletrack rims at smaller PCD's than 5 on 5.5"
But I HAVE found somewhere. Real Wheel in Indiana US. This guys do lots of speedway rims and such, but also supply the mud drag guys which is why they offer narrow beadlocked fitments in 5 on 5.5 PCD.
http://www.realwheel.net/products.php?catid=17
These guys will do 15X4 right up to 15X20 with an outer beadlock.
They'll do a 15X8 up with an inner and outer beadlock.
As you'd imagine they aren't cheap. A 15X6 with an outer beadlock, 3" Backspaced is USD $580
A 15X8 double beadlocked, 3" backspaced is USD$760
So whilst these will have limited appeal, they DO exist - and it sounds like they got going out of frustration with poor delivery from (perhaps) Marsh. It's certainly a very similar product to what Marsh used to offer, if not with the carbon fibre.
Based on the pricing from Jackson Motorsport and Real Wheel, you'd be looking a AUD$1180 per corner + freight. Ouch.