I like Michael Flynn’s *Firestar *series. It’s very near-future science fiction (rapidly becoming alternate history) about the development of a private space program, spearheaded by a wealthy businesswoman who has a secret fear of a planet-killing asteroid impact and is desperate for mankind to develop the technology to defend itself against one. The first book reminds me of The Right Stuff, with engineers developing reusable spacecraft intended to reach low earth orbit and return, and the test pilots who are eager to fly them.
Another source for hard sci-fi is TV Tropes’s section on “Mohs Scale of Science Fiction Hardness”. From there, I found this webpage with its own gradation of science fiction hardness, and more importantly, lots of examples.
Van Vogt is anything but Hard-Core SF. He may be better remembered as the spokewriter for woo. A different tack, maybe, I would suggest book re-editions published by NESFA press (NESFA Press – NESFA). They specialize in reprinting older out-of-print SF and that might be an attraction in itself.