Yeah RS components is a hassle when you don't have an account with them and there seems to be a bit of confusion.
However you can buy over the counter, just go and tell them its over the counter sales. I ordered an ATMega328 that way. I phoned in to the Montague Gardens branch, told them i'm buying over the counter and then had to go in to pay for the part. Since they just added Arduino to their catalog at that point, they never had stock and it took about 2 weeks. I paid around R42 excl for the part, but now I see its jumped up to over R60.
If you are in Cape Town and want to build the ZArdino clone the PCBs are being made up as we speak so PM me and I will point you to the supplier.
Otherwise try Netram since they will probably be a lot easier, and they were doing it before RS added it to their catalog.