I have had good luck using "Manila Hemp" rope which has been soaked and untwisted. That's the material used to make typical "Hemp" rope which you can find nearly anywhere. It's actually "Abaca" or banana leaf fibre. It's very strong and has the required "green" look with small dark flecks and streaks mixed in.
I have experimented with various epoxies and all seem to work pretty well. There is quite alot of similarities across the types offered by various companies.
I really liked the MAS resin. Good price and seemed virtually odorless and free of "fumes".
I'm actually really interested in trying some Poly Epoxy from Aircraft Spruce. It is fully twice as strong in every way above all the other types of Epoxy out there.
It makes sense to me that the apparent drawbacks of natural fibre breaking down over time (as demonstrated by the bamboo bike studio) could be offset by doubling the matrix binder strength.