There are recordings of David Munrow etc with early renaissance music on them that may be still available, and may be suitable.
On the question of When was Arthur, I have heard it suggested that Arthur should be dated to the end of the bronze age as the (so called) "magic" sword Excalibur was simply the arrival of an Iron sword and its strength compared to Bronze would have appeared like Magic, also "the Lady of the lake" is a reference to the "tempering" in the water, and that the True King who could" draw the sword from the stone" was the the person that new the secret of smelting iron!!!!!!!