Have you tried emailing Ernie Ball?
I'm a huge fan of the EBMM Sterling, having a 4HH with a matching headstock.
Anyway - it seems they've stopped making the Sterling and it's not available via the customisation tool either.
I was curious as to whether I could get myself another Sterling 4HH to my specs so I emailed them.
I got a quote about 4 days later for an ex-works price for what I had specified.
Once I added shipping and import taxes and fees we were looking at north of £3.5k! - a bit rich for me but they did quote and would do it.
Perhaps they'd do the same for a Bongo special.