Just buy monorails for the bridge. Or you can call up any number of companies and get a quote on a custom bridge.

The other hardware should all be easy to find.

I am just a beginner, so I dont know too much about the bass. i have been taking lessons for a couple months so i know enough to express my opion on this situation. I think there should only be a 4 string bass. that is what makes it so unique. the fact of the bass coming to be 5 6 7 and 12 string bass, i think, is just dumb. they change too many things and rearange to many stuff and they are the best the way they were first made. it has the unique deep sound making it sound like the grandfather of guitars. it is (in my perspective) the best insterment. but thats enough of my time so i will let u debate on the situation.
-Dave

Your statement is like saying "I've been reading up on nuclear physics for the past 3 weeks, I'm going to now go build myself a cold fusion plant."

neither my 4 nor my 6 string sound like a guitar grandpa and that's fine ;-|

Maybe you should try owning a bass with more then 4
strings before you make up your mind about this. It's not
enough to go to the nearest store and try a 5 or 6 string
bass for a few minutes. No offence, but you can't make up
your mind about something you don't know anything about.

Thor.

I think everyone has his or her own opinion about their own "insterment" and yours is stupid. I'm just kidding. But be a little more open minded especially if you've only been playing a few months, have you ever heard that lush 8 string sound?

you could use 2 4 string bridges

You can't. Youll have a big gap off between the middle strings if you do.