Ok, I'm not sure about where to get them done, but I'll give you this advice - DON'T BOTHER.
It's not the fact that it's dangerous abroad, whoever does them may well have safety and cleanliness certificates and be cleaner than some back home. It's just that when you get a Tattoo, your skin becomes really tender in the area and not only will it be more dangerous in the harmful rays, but the sun on a brand new tattoo can also fade the colours quite considerably. So instead of your beautiful black Celtic cross, you could end up with a grey blurry one.
Another thing to consider, is that when getting a tattoo, your skin bleeds so after a day or so, it scabs over for about two weeks (don't pick the scabs cos this effects the colour also) and in that time it looks shite.
I would recomend getting a tatt at least 3 weeks before you go on your hols. That will give your skin time to heal, and it will look the part too.
I'm no expert, but I've got a few tattoos and my mate knows quite a bit about them, and this is advice he's given me.