Re:
Generally speaking I find getting hold of decent retro amberwalls one of the hardest and sometimes costly, mainly as they are a consumable item and 25 year old rubber doesn't fair well.
I like to keep all the tyres on my retro fleet from the era, these include, Panaracers Dart/Smoke, IRC Mythos, Maxxis, WTBs and also Tioga. I can honestly said the Tiogas don't seem to fair well, they turn to sort of foam and just crumble! The Panaracers tend to dry out and crack between the knobs and carcass, I find the IRCS fair pretty well.
HOWEVER this is for general gentle riding, woods, toepaths, road etc. If I were to attempt to ride any of the retros to the limit, I would seriously need to consider modern rubber for the pure safety issue and that modern rubber is twice as grippy than older, not only in design but the fact it hasn't dried out.