Hmm, you could get heavy linen thread for leather working or hand bookbinding. Then wax it with bees wax and roll/twist several strands together to make a thin rope. It would give you a thin strong rope which could be taken apart later to the original threads and used like the inner strands of 550 cord. It would require an awful lot of extra work and expense though. Also, while you may have trouble finding hemp rope, hemp thread is pretty easy to find for various uses at craft stores.