Sooze, yes you can buy HRT over the counter and without a prescription in Gibraltar.
They sell UK branded products like Estrogel and I have bought patches there for other people in the past. One word of advice, don't try to buy HRT in the pharmacy in Morrisons because they ask for a prescription but there is no problem in Main Street where most of the pharmacies are located.
Once in Gibraltar, you can easily walk over the border into Spain (La Linea) where pharmacies and HRT supplies are plentiful!