Was black ever an interior option on those trucks? I have only seen tan and grey. anyway, I think the company SEM has an interior dye for seat belt webbing. I dont know where they get it, but interior shops can get the belts in any color as well as carpets in any color.Good Luck anyways you do it
If you look in the some of the truck mags they have a ads in there for places to buy all kinds of parts i think the names CK Resto & LMC. Also try ebay or craigslist for your area you live.
Maybe black wasn't an option..the only reason I was wondering is because CK resto offers black OEM replacement carpet, headliner, sun visors, and door panels..hopefully I won't have to dye them, but that's the way it's looking..