RailAir link Reading-Heathrow ticket purchase

Every year in the past I have been able to buy a ticket in advance for the Reading-Heathrow bus for the day of my travel, paid for online and sent by email. This year for the first time the old site diverts to First Bus, which still sells the tickets but won't allow me to proceed with purchase without a UK address. There is no option to select "overseas" and they don't need the address anyway given that the e-ticket is sent by email. After some searching I found an email address for them and have sent a request for help, but meanwhile has anyone else encountered this problem and found a workaround? It used to be so easy!