A lot of the shows I’d consider “hard to find classics” are actually on streaming at this point in various ways (hell, even Utena is free on Nozomi’s YouTube channel) but I don’t have time to check all the different services because I’m writing this right before starting a shift at work.
Anyways, here’s my short list:
Kimagure Orange Road - 1980’s supernatural/love triangle slice of life. Hella style.
The Irresponsible Captain Tylor - an early 90’s comedic send up to space opera classics like Space Battleship Yamato (also worth watching!) about the captain of a space vessel who may be either a tactical genius or a complete buffoon.
Reach For The Top!! Gunbuster!! - very well known, but very hard to find (legally) in it’s original OVA form. Anno’s super-robot send up before Evangelion. A little lighter in tone, but dealing with some of the same themes in (imo) some more interesting ways. Definitely also watch the sequel, Diebuster, which is a personal favourite of mine and easier to find streaming. Unfortunately, Gunbuster is required viewing.
Dragon’s Heaven - 1980’s mecha OVA with a really distinct style and I can’t determine if it’s due to lack of budget or unique artistic vision. Either way, a great watch.
Space Runaway Ideon - Tomino’s post-Gundam mecha series from 1980.
I’ll absolutely co-sign Patlabor and Hidamari Sketch.