Don't worry you're not alone...

The BMX carbon forks I looked at, had the following shortcomings:
* Looked too BMX-y for my Swift
* The ones which were OK for my weight are too heavy, hardly any saving over the stock fork
* The ones which were light enough were only rated for juvenile weight riders
* then there is the dropout-to-crown length, which for the Swift is rather long, so a tight BMX fork ruins the geometry and will make the bike's top tube slope down

I give you this list just so you don't end up buying something which might not work.

I have also looked into shortening a carbon roadie fork, but ran up against the problem of the dropouts ending up too close to each other.

I am wondering if it's worth approaching a frame builder... nice lightweight Reynolds 953 fork...