All: If you have an older car with R12, your not locked out by not being able to buy the R12. First, although they tell you that you "can't", you can convert your R12 system over to 134, if you want to, without evacuating the system of R12. It does require a oil addition for the 134 and then putting 134 in, instead of R12.
Their are several brands of refrigerant which are similar to R12, in terms of their characteristics, but they aren't manufactured by DuPont. You can buy a product called RedTek, over the internet and they will ship the can's to you. It uses the same fittings and adapters as R134, but it takes less refrigerant, it will run on the oil in R12 systems and it doesn't require a license. I've done both the R134 and the RedTek and the RedTek does seem to be more efficient.
Anyway, the point is that their are alternatives avialable, but they aren't as widely known as R134, but they seem to work fine.
You're absolutely right. Where most people screw up is not changing the compressor oil when they convert to 134.