Since they don't appear to be on Hoopla your best bet might be trying an Inter-library loan for the "Marvel Masterworks: Golden Age Captain America" books. This page should have all the information you would need for the request, though check with your library for the specific method https://www.marvel.com/comics/collection/39345/marvel_masterworks_golden_age_captain_america_vol_1_trade_paperback
As a heads up, Marvel has only reprinted issues 1-20 and 76-78 of the original "Captain America Comics" series. You specifically mentioned Jack Kirby in your post, so if you're only interested in stuff he worked on you're fine, as he only did issues 1-10 and then left Timely until he returned in the late 50s or early 60s. But if you're interested in the entirety of the Golden Age stories then the only way currently to read pages 21-75 are to purchase physical versions (which is impossible for most people) or pirate them.