Hi petnes,
You can check
www.ppjn.com for example. Here you can find the type of aircraft comprising the fleet various airlines operate. I think it's a very useful site. Or
www.pilotinterviews.com. However I'm not sure if the info contained on this site is totally up to date, or 100% correct. There are various sites on the internet where you can find this kind of info. Or you can just visit the website of the airline you're interested in. The always have a part where you can see which types they operate.
Hope this is somewhat useful to you. Good luck!!
Ciao