Yes, 8 speed is getting scarce, but have there ever been any mainstream 8 speed 11-36 cassettes?
Sheldon Brown's page on 8 speed cassettes lists 11-34 as the on with the largest cog. You can try building a custom one (e.g., take an 11-32, add a 36 from another cassette to the bottom and replace 11 and 13 with a top position 13).
Also, these days there are new wide range cassettes - for example, Shimano 11-40 HG400:
https://www.treefortbikes.com/Shiman...8-Speed-11-40t or even cheaper Sunrace equivalent:
https://www.amazon.com/Race-CSM680-8.../dp/B01N7VRAFM
You may need an extender for the RD hanger, maybe a new RD with a higher capacity. OTOH 11-40 will be a more significant improvement compared to 11-36.