I have the same (older style) Hope headset on my HT. I recently lost the tapered ring and couldn’t find one anywhere, called Hope and they had one in the post to me the same day, very, very impressed top people to deal with 🙂
Unfortunately I think the bearings for the older headsets like yours were a custom size specially made for Hope, so you can’t buy them aftermarket, and Hope had run out. On a plus note I think Hope were exchanging old headsets for the new style for around £25 when the bearings went. Let us know how you get on, as interested to know if they still offer this…