Impossible to say exactly.
Without taking measurements, it's very likely it's:
MnZn ferrite
mu >= 500
Fo > 1MHz
Bmax >= 0.3T
Further, it might be very similar to a Fair-Rite #77 (generic all-purpose, mu=2000), or #33 (lower mu, near zero tempco).
It's unlikely to be very high mu (doesn't matter a damn for a rod; low cutoff frequency), or NiZn (lower Bmax which won't matter, but higher cost and lower mu will matter).
If you want more, Amidon does indeed have #33 rods in various sizes.
Tim