Is Indian food easily available in European countries?

In big cities like that, you could probably find an Indian or a few Indian restaurants (if you know where they are), although I'm not sure about all of them. I suggest googling for Indian restaurants in these cities and look where they are, as they won't have one on every corner.

Quality: don't expect it will (always) be the actual same food as in India itself. It will probably be made with more products the European people are more familiar with.

Price: the price will be a lot more than in India, because it's just not India. Everything is more expensive. Especially in big cities. For example: a soda in a bar in the center of Paris will already be more than 5 euros.

Alternative: I don't know if you are staying in a hotel are renting an apartment or such, because then you could go to small local Indian supermarkets and prepare the food yourself.

When I left the UK to live in germany I missed Indian food more than anything.

These days it's easy: Google is your friend. There are Indian restaurants everywhere. If you check out Trip Advisor you will even get reviews, though they are sometimes suspect.

I've definitely eaten Indian food in Paris (was a few years back so don't remember exact location). Can't speak for the other places.

But I'm sure it won't be like it is at home - they'll have adapted things to fit local tastes - it's sound business.

If they only like spicy things they could try Moroccan or Turkish. But as they saying goes, when in Rome...

The UK wasn't one of the destinations you mentioned, but I suspect the situation is similar. Firstly, most UK restaurants describing themselves as Indian are in fact Bangladeshi or Pakistani run. Secondly, the food you get served there is nothing like the food you get in India (or, as I've been told, Pakistan or Bangladesh). The main differences (to my palette and various friends who live or have lived in India) are: there's no subtlety in the spice, everything tastes like the same mix of spices with the amount of heat varied, many of the dishes are too rich, and far fewer of the dishes are vegetarian. And few of them are authentic; "Indian" restaurants in the UK aren't bad as such - just they don't serve the food you'd find in India (having been a few times). Advice from Indian friends is that in the UK if you want Indian food, you are best looking for something from a named region of India, and preferably vegetarian. For instance, Govinda's Krishna restaurant in Soho is (allegedly) reasonably authentic, as you might expect from somewhere attached to a temple; perhaps look for somewhere similar in the cities you mention?

I've eaten in "Indian" restaurants in the US and elsewhere in Europe, though not the specific cities you mention. Based on this, I would suspect if anything that the destinations you are planning to visit would be worse than the UK, as the UK has a far larger minority from the Indian subcontinent. You'd be best to carefully investigating restaurants catering to that group. In that respect, I would suggest your parents are going to be disappointed.

However, if I went to India and asked for a fillet steak, I would also be disappointed. France is the culinary capital of Europe. Having persuaded a Sri Lankan who thought all European food too bland without extra chilli added of the merits of French food by taking them to a good French restaurant, I'd humbly suggest that you might be better persuading them to try the local food. One strategy might be to take them to the first "Indian" restaurant you find, which I suspect may instantly encourage them to broaden their horizons!

If it's anything like Australia: ask a taxi driver!

We have many Indian taxi drivers here and they always know the best, cheapest Indian restaurants. I'm from the UK and I know the situation is the same there, but I'm not so sure about mainland Europe, sorry.

I've travelled a lot, and it is definitely always possible to find Indian food. You want to avoid the fancy restaurants and work out where the local Indians go. How do you get in touch with local Indians in the cities you're travelling to?...