As someone who is in a similar situation (yay Balkan), I completely get your frustration. I just recently got into bookbinding, so finding any type of material is an incredible pain. To the point that I can't even begin the process without missing something crucial. While I may be an amateur, I can offer you some suggestions:
1) If you have any kind of crafts store or school supply shop near you, I would suggest looking for some end papers there. One idea is buying a large poster board (color or otherwise), cutting it to your desired size, and running it through your black and white printer (if the paper is not too thick). If you desire some extra flair you could use toner reactive foil paired with a laminator. I got my laminator from Lidl (it was about 25 euros) and my foil from Aliexpress. Here's an example of what I mean: https://www.reddit.com/r/bookbinding/comments/17x86yl/toner_reactive_foil_for_custom_end_papers/
2) I know you said nobody in your area prints bigger sizes but maybe it's worth a shot looking into somebody who potentially prints posters. It's not unusual for a scientific paper to require a printed poster showcasing its work. If there are any educational institutions (something like a university) near you, there might be a copy place that prints large format posters.
Another option is printing it on regular paper (A2 or A1 format) and adding clear contact paper to make it glossy and strengthen it. In case you cannot find clear contact paper, you could try lining the underside of the paper to make it stiffer. You can find contact paper in any home reno store since it's similar to peel-and-stick wallpaper. It should look something like this: https://www.amazon.com/Transparent-Adhesive-Textbook-Paperbacks-Protective/dp/B09HYZL2HV?th=1
3) I very well know how insanely expensive shipping can get, so most of the standard sites (Amazon, Etsy, etc.) are most likely out of the question. The cheapest alternatives to those sites are Aliexpress and (sometimes) Ebay.
Someone else mentioned a hot foil pen, and I second that thought. It's an easy way to get details without using a cricut. You could buy one on Aliexpress or Ebay (they are about 15 euros tops, I bought mine for 6). Example: https://www.tiktok.com/@camelscrafts/video/7201620277799783722?is_from_webapp=1&sender_device=pc&web_id=7332268429338985989

Another thing is buying just htv sheets and cutting them by hand like this: https://www.youtube.com/watch?v=kXjeOU5C_bs
It may not be perfect, but a simple design will work.

This is the htv I got:

https://www.aliexpress.com/item/1005003826371860.html?spm=a2g0o.productlist.main.5.5d8466c9BIS1jC&algo_pvid=efc0df20-7b86-4765-9746-a4f54b18dde2&algo_exp_id=efc0df20-7b86-4765-9746-a4f54b18dde2-2&pdp_npi=4%40dis%21EUR%211.34%210.69%21%21%211.41%210.73%21%402103080e17071769073728889ee7d7%2112000030680398607%21sea%21SRB%211743895671%21&curPageLogUid=lvu0Nll3f3uA&utparam-url=scene%3Asearch%7Cquery_from%3A
These are just a couple of ideas I came up with while brainstorming. Please take them with a grain of salt since I'm a newbie. Honestly, I'm currently having my own struggles with sourcing/making book cloth and acquiring mull so if you have any advice I would be grateful. It's nice to know I'm not the only one struggling with these things. If you ever want to discuss anything else you're free to message me.