It still exists but you might have to go to Cyprus to get it! Hirondelle has (rightly) fallen out of favour with UK wine drinkers and it's unlikely that anyone still imports it.
The sweet taste of Hirondelle is now generally only enjoyed by most people when it accompanies a sweet dessert (and there are many better quality wines which can fulfil this role).
The producers of Hirondelle have never named the grape variety on the label but it's likely that it will be Muscat (or a blend containing Muscat). So if you're looking for something similar, that's the grape you should be looking for. I suggest that, the next time you're in Tesco, you pick up a bottle of Tesco Moscatel de Valencia (dirt cheap) or, for rather better quality, Brown Brothers Moscato.
Hoping this helps,
Chris