Try Ross Roses in SA. They have access to all remaining plants at the old Thomas 4 Roses nursery, and will custom graft any of them - if the plant still exists and is large enough to take material from.

'Tassin' is still listed at T4R, but they did lose quote a few plants in the droughts and fires a few years back (just before they retired from business). I don't know if 'Tassin' survived.

Of course, the catch with getting one custom-grafted is that he would have to wait until he was 91 to get his hands on the bush. If he's planning on living to 100, no problem. :)