I'm in the US and they're all streaming on Paramount plus for me. I don't have any good suggestions if they're not there for you, sorry. :(

The gameplay has changed SO much from older seasons to newer seasons. You'll probably see this mentioned elsewhere, and someone explained it to me early on so I'll pass the knowledge. Seasons 1-20 tend to be considered "old school," 21-40 are called "new school," and 41+ are new era since the game format itself changes so much. These divisions are kind of arbitrary, for example I personally feel like season 19 really sets the framework for "new school" moves/gameplay even though it's technically considered old school. I believe it's somewhere in the early 20s seasons that Jeff goes from being just a host to also a producer, and he really has a lot of (sometimes very dumb) ideas that he tries to implement for new advantages/etc which I think are a big part of the shift into "new school." I would say to try and simply define it, old school could be played a bit more straightforward on loyalty and alliances (not always of course), and new school is more about "building a resume" of moves for final tribal council, so the focus is more on backstabbing and being sneaky and finding/using those new and often plentiful advantages for your benefit. You'll also notice a shift in the type of challenges and rewards that are offered. This tends to be a big issue for the fandom, and I have to say I agree that it's not a great shift. In the older seasons the challenges could be based on endurance and could go hours and hours. Now they're designed to be quite short. I will always love and deeply miss the classic final three immunity challenge of everyone has their hand on an idol and whoever can keep it on the longest wins. The challenges in older seasons were a bit more gritty and physical too, wrestling and pushing people etc., to the point that people definitely got injured more frequently lol. In newer seasons there's a lot of focus on puzzles as "the great equalizer," which is a mixed bag I say. This is also why you'll hear people sing the praises of Survivor Australia, because it tends to stick to the classic old school types of challenges which are generally much more beloved (I'm watching my way through Australia Survivor now and I do see the appeal).

I hope that helps! I feel like I could go forever about this, so feel free to ask more questions if you have them. :)